Add request's reserved client and target client id

This patch defines the request's reserved client and the target client
id. The reserved client of a request is set to an environment or an
environment settings object during a navigation or a worker creation
request, respectively. The target client id of a request is set to the
target browsing context's active document's environment settings
object's id during a navigation. The given values are primarily used
to provide the reserved client's id and target client's id to service
workers' fetch event handlers.

This removes the request's target browsing context as the reserved
client provides the same information.

Related issue: w3c/ServiceWorker#870
Related change: whatwg/html#1776

Overview.html

@@ -7,7 +7,7 @@
 
 <p><a class="logo" href="https://whatwg.org/"><img alt="WHATWG" height="100" src="https://resources.whatwg.org/logo-fetch.svg" width="100"></a>
 <h1 id="cors">Fetch</h1>
-<h2 class="no-num no-toc" id="living-standard-—-last-updated-17-october-2016">Living Standard — Last Updated 17 October 2016</h2>
+<h2 class="no-num no-toc" id="living-standard-—-last-updated-24-october-2016">Living Standard — Last Updated 24 October 2016</h2>
 
 <dl>
  <dt>Participate:
@@ -731,6 +731,26 @@ <h4 id="requests"><span class="secno">3.1.5 </span>Requests</h4>
 <dfn data-dfn-for="request" data-export="" id="concept-request-client" title="concept-request-client">client</dfn> (null or an
 <a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#environment-settings-object">environment settings object</a>).
 
+<p>A <a href="#concept-request" title="concept-request">request</a> has an associated
+<dfn data-dfn-for="request" data-export="" id="concept-request-reserved-client" title="concept-request-reserved-client">reserved client</dfn>
+(null, an <a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#environment">environment</a>, or an
+<a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#environment-settings-object">environment settings object</a>). Unless stated otherwise it is null.
+
+<p class="note no-backref">This is only used by <span>navigation requests</span> and worker
+requests, but not service worker requests. It references an
+<a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#environment">environment</a> for a <a href="#navigation-request">navigation request</a> and an
+<a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#environment-settings-object">environment settings object</a> for a worker request.
+
+<p>A <a href="#concept-request" title="concept-request">request</a> has an associated
+<dfn data-dfn-for="request" data-export="" id="concept-request-target-client-id" title="concept-request-target-client-id">target client id</dfn>
+(a string). Unless stated otherwise it is the empty string.
+
+<p class="note no-backref">This is only used by <span>navigation requests</span>. It is the
+<a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#concept-environment-id" title="concept-environment-id">id</a> of the
+<a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#concept-environment-target-browsing-context">target browsing context</a>'s
+<a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/browsers.html#active-document">active document</a>'s
+<a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#environment-settings-object">environment settings object</a>.
+
 <p>A <a href="#concept-request" title="concept-request">request</a> has an associated
 <dfn data-dfn-for="request" data-export="" id="concept-request-window" title="concept-request-window">window</dfn>
 ("<code>no-window</code>", "<code>client</code>", or an
@@ -745,10 +765,6 @@ <h4 id="requests"><span class="secno">3.1.5 </span>Requests</h4>
 explicitly set <a href="#concept-request" title="concept-request">request</a>'s
 <a href="#concept-request-window" title="concept-request-window">window</a>.
 
-<p>A <a href="#concept-request" title="concept-request">request</a> has an associated
-<dfn data-dfn-for="request" data-export="" id="concept-request-target-browsing-context" title="concept-request-target-browsing-context">target browsing context</dfn>
-(null or a <a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/browsers.html#browsing-context">browsing context</a>). Unless stated otherwise it is null.
-
 <p id="keep-alive-flag">A <a href="#concept-request" title="concept-request">request</a> has an associated
 <dfn id="keepalive-flag">keepalive flag</dfn>. Unless stated otherwise it is unset.
 

fetch.bs

@@ -29,6 +29,9 @@ urlPrefix: https://html.spec.whatwg.org/multipage/
                 text: ancestor browsing context
                 text:origin
                     for:browser
+            urlPrefix: webappis.html
+                text:environment
+                text:environment id
 url:https://html.spec.whatwg.org/multipage/webappapis.html#https-state;spec:html;text:HTTPS state;type:dfn
 url:https://w3c.github.io/webappsec-referrer-policy/#enumdef-referrerpolicy
     type:interface
@@ -746,6 +749,26 @@ outlawing <a>forbidden methods</a> and
 <dfn data-export for=request id=concept-request-client>client</dfn> (null or an
 <a spec=html>environment settings object</a>).
 
+<p>A <a for="/">request</a> has an associated
+<dfn id=concept-request-reserved-client data-export for=request>reserved client</dfn>
+(null, an <a spec=html>environment</a>, or an
+<a spec=html>environment settings object</a>). Unless stated otherwise it is null.
+
+<p class="note no-backref">This is only used by <a>navigation requests</a> and worker
+requests, but not service worker requests. It references an
+<a spec=html>environment</a> for a <a>navigation request</a> and an
+<a spec=html>environment settings object</a> for a worker request.
+
+<p>A <a for="/">request</a> has an associated
+<dfn id=concept-request-target-client-id data-export for=request>target client id</dfn>
+(a string). Unless stated otherwise it is the empty string.
+
+<p class="note no-backref">This is only used by <a>navigation requests</a>. It is the
+<a lt="environment id" spec=html>id</a> of the
+<a spec=html>target browsing context</a>'s
+<a spec=html>active document</a>'s
+<a spec=html>environment settings object</a>.
+
 <p>A <a for="/">request</a> has an associated
 <dfn data-export for=request id=concept-request-window>window</dfn>
 ("<code>no-window</code>", "<code>client</code>", or an
@@ -760,10 +783,6 @@ outlawing <a>forbidden methods</a> and
 explicitly set <a for="/">request</a>'s
 <a for=request>window</a>.
 
-<p>A <a for="/">request</a> has an associated
-<dfn data-export for=request id=concept-request-target-browsing-context>target browsing context</dfn>
-(null or a <a spec=html>browsing context</a>). Unless stated otherwise it is null.
-
 <p id=keep-alive-flag>A <a for="/">request</a> has an associated
 <dfn>keepalive flag</dfn>. Unless stated otherwise it is unset.