Add Network module

This is designed to support logging network requests. Important use
cases include:

* Determing if a specific network request occured
* Monitoring request performance
* Generating a HAR file for offline analysis of requests

This does not currently attempt to support network request
interception (i.e. mutable access to requests), but the intent is that
the same lifecycle events could be used in a blocking way.

It also currently only supports HTTP-type requests and not
e.g. WebSockets. Some support for integration with service workers is
also missing.

The typical order of events is

network.beforeRequestSent - before request is sent, would later be the
right point to change the request headers or body or prevent the
request entirely.

network.responseStarted - after response headers are received, but
before body. Would later be a point to override the response headers
or body.

network.responseCompleted - after the request is fully complete.

network.fetchError - After any error that will prevent the request
from completing.

Compared to CDP this is missing an event for data being
received. Compared to WebExtensions, this is missing an event after
the headers are sent but before the data is sent.

Author: jgraham

index.bs

@@ -253,7 +253,9 @@ Command = {
 
 CommandData = (
   SessionCommand //
-  BrowsingContextCommand
+  BrowsingContextCommand //
+  NetworkCommand //
+  ScriptCommand
 )
 
 EmptyParams = { *text }
@@ -286,6 +288,7 @@ ResultData = (
   EmptyResult //
   SessionResult //
   BrowsingContextResult //
+  NetworkResult //
   ScriptResult
 )
 
@@ -298,8 +301,9 @@ Event = {
 
 EventData = (
   BrowsingContextEvent //
-  ScriptEvent //
-  LogEvent
+  LogEvent //
+  NetworkEvent //
+  ScriptEvent
 )
 </pre>
 
@@ -3631,6 +3635,271 @@ opened</dfn> steps given |window|, |type| and |message|.
 
 </div>
 
+## The network Module ## {#module-network}
+
+The <dfn export for=modules>network</dfn> module contains commands and events
+relating to network requests.
+
+### Definition ### {#module-network-definition}
+
+<pre class="cddl remote-cddl">
+
+NetworkCommand = (
+)
+
+</pre>
+
+[=local end definition=]
+
+<pre class="cddl local-cddl">
+
+NetworkResult = (
+)
+
+NetworkEvent = (
+    NetworkBeforeSendRequest //
+    NetworkResponseStarted //
+    NetworkResponseCompleted //
+    NetworkError
+)
+
+</pre>
+
+### Types ### {#module-network-types}
+
+#### The network.Cookie type #### {#type-network-Cookie}
+
+[=Remote end definition=] and [=local end definition=]
+
+<pre class="cddl local-cddl">
+NetworkCookie = {
+    name: text,
+    ? value: text,
+    ? binaryValue: [ uint ]
+    domain: text,
+    path: text,
+    expires: uint,
+    size: unit,
+    httpOnly: boolean,
+    secure: boolean,
+    session: boolean,
+    sameSite: "strict" / "lax" / "none",
+};
+</pre>
+
+The <code>NetworkCookie</code> type represents a cookie.
+
+If the cookie value can be represented as a UTF-8 encoded string, the
+<code>value</code> field will be present. Otherwise the <code>binaryValue</code>
+field will be present and consist of an array of integers representing the bytes
+of the cookie value.
+
+#### The network.FetchTimingInfo type #### {#type-network-FetchTimingInfo}
+
+[=Remote end definition=] and [=local end definition=]
+
+<pre class="cddl local-cddl">
+NetworkFetchTimingInfo = {
+    requestTime: uint,
+    redirectStart: uint,
+    redirectEnd: uint,
+    fetchStart: uint,
+    dnsStart: uint,
+    dnsEnd: uint,
+    connectStart: uint,
+    connectEnd: uint,
+    tlsStart: uint,
+    tlsEnd: uint,
+    requestStart: uint,
+    responseStart: uint,
+    responseHeadersEnd: uint,
+    responseEnd: uint,
+};
+</pre>
+
+The <code>NetworkFetchTimingInfo</code> type represents the time of each part of
+the request, relative to <code>requestTime</code>.
+
+TODO: Add service worker fields
+
+#### The network.Header type #### {#type-network-Header}
+
+[=Remote end definition=] and [=local end definition=]
+
+<pre class="cddl local-cddl">
+NetworkHeader = {
+    name: text,
+    ? value: text,
+    ? binaryValue: [ uint ]
+};
+</pre>
+
+The <code>NetworkHeader</code> type represents a single request header.
+
+If the header value can be represented as a UTF-8 encoded string, the
+<code>value</code> field will be present. Otherwise the <code>binaryValue</code>
+field will be present and consist of an array of integers representing the bytes
+of the header.
+
+#### The network.Initiator type #### {#type-network-Initiator}
+
+[=Remote end definition=] and [=local end definition=]
+
+<pre class="cddl local-cddl">
+NetworkInitiator = {
+    type: "parser" / "script" / "preflight" / "other",
+    ?columnNumber: uint,
+    ?lineNumber: uint,
+    ?stackTrace: StackTrace,
+    ?request: NetworkRequest
+};
+</pre>
+
+The <code>NetworkInitiatior</code> type represents the source of a network request.
+
+TODO: Align more closely with Fetch here?
+
+#### The network.Request type #### {#type-network-RequestId}
+
+[=Remote end definition=] and [=local end definition=]
+
+<pre class="cddl local-cddl remote-cddl">
+NetworkRequest = text;
+</pre>
+
+Each network request has an associated <dfn export>request id</dfn>, which is a string
+uniquely identifying that request.
+
+#### The network.RequestData type #### {#type-network-RequestData}
+
+[=Remote end definition=] and [=local end definition=]
+
+<pre class="cddl local-cddl">
+NetworkRequestData = {
+    url: text,
+    method: text,
+    headers: [ *NetworkHeader ],
+    cookies: [ *NetworkCookie ],
+    ?body: text,
+    bodySize: uint,
+    headersSize: uint
+};
+</pre>
+
+The <code>RequestData</code> type represents an ongoing network request.
+
+TODO: Body is actually bytes, not clear how to handle it as text
+
+#### The network.ResponseData type #### {#type-network-ResponseData}
+
+[=Remote end definition=] and [=local end definition=]
+
+<pre class="cddl local-cddl">
+NetworkResponseData = {
+    url: text,
+    protocol: text,
+    status: unit,
+    statusText: text,
+    headers: [ *NetworkHeader ],
+    cookies: [ *NetworkCookie ],
+    mimeType: text,
+    bytesReceived: uint,
+    timings: NetworkFetchTimingInfo,
+};
+</pre>
+
+### Events ### {#module-network-events}
+
+#### The network.beforeRequestSent Event #### {#event-network-beforeSendRequest}
+<dl>
+   <dt>Event Type</dt>
+   <dd>
+      <pre class="cddl local-cddl">
+        NetworkBeforeRequestSentEvent = {
+         method: "network.beforeRequestSent",
+         params: NetworkBeforeRequestSentParams
+       }
+
+       NetworkBeforeRequestSentParams = {
+        request: NetworkRequest,
+        navigation: Navigation / null,
+        context: BrowsingContext / null,
+        requestData: NetworkRequestData,
+        initiator: NetworkInitiator
+        timestamp: number,
+       }
+      </pre>
+   </dd>
+</dl>
+
+#### The network.fetchError Event #### {#event-network-fetchError}
+
+<dl>
+   <dt>Event Type</dt>
+   <dd>
+      <pre class="cddl local-cddl">
+        NetworkFetchErrorEvent = {
+         method: "network.fetchError",
+         params: NetworkFetchErrorParams
+       }
+
+       NetworkFetchErrorParams = {
+        request: NetworkRequest,
+        errorText: text,
+        timestamp: number,
+       }
+      </pre>
+   </dd>
+</dl>
+
+#### The network.responseCompleted Event #### {#event-network-responseCompleted}
+
+<dl>
+   <dt>Event Type</dt>
+   <dd>
+      <pre class="cddl local-cddl">
+        NetworkResponseCompletedEvent = {
+         method: "network.responseCompleted",
+         params: NetworkResponseCompleteParams
+       }
+
+       NetworkResponseCompletedParams = {
+        request: NetworkRequest,
+        navigation: Navigation / null,
+        context: BrowsingContext / null,
+        responseData: NetworkResponseData,
+        timestamp: number,
+       }
+      </pre>
+   </dd>
+</dl>
+
+After the full response body is received.
+
+#### The network.responseStarted Event #### {#event-network-responseStarted}
+
+<dl>
+   <dt>Event Type</dt>
+   <dd>
+      <pre class="cddl local-cddl">
+        NetworkResponseStartedEvent = {
+         method: "network.responseStartedEvent",
+         params: NetworkResponseStartedParams
+       }
+
+       NetworkResponseStartedParams = {
+        request: NetworkRequest,
+        navigaton: Navigation / null,
+        context: BrowsingContext / null,
+        responseData: NetworkResponseData,
+        timestamp: number,
+       }
+      </pre>
+   </dd>
+</dl>
+
+After the response headers are received but before the body.
+
 ## The script Module ## {#module-script}
 
 The <dfn export for=modules>script</dfn> module contains commands and events