[WIP] JavaScript Realm proposal integration

This patch gives the TC39 JavaScript Realm proposal semantics in HTML.
Realms are given an environment settings object, which is especially
meaningful for module loading. Other aspects of the environment
settings object may be unreachable because Realms do not contain Web
APIs, but in general, Realms inherit their settings from the outer
environment.

Overall, the semantics of Realms are analogous to a same-origin iframe
without any Web APIs, just what JavaScript provides. When modules are
used in Realms, module specifiers are interpreted with respect to the
base URL of the surrounding environment, but when a module is imported
within a Realm, it is a separate copy from what may be loaded in the
surrounding environment or other Realms.

The Realm proposal is currently at Stage 2, and this patch should not
land until, at the earliest, the proposal is at Stage 3.

source

@@ -3046,6 +3046,14 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
  <li>The <dfn data-x="js-HostGetImportMetaProperties" data-x-href="https://tc39.es/proposal-import-meta/#sec-hostgetimportmetaproperties">HostGetImportMetaProperties</dfn> abstract operation</li>
  </ul>
 
+ <p>User agents that support JavaScript must also implement the <cite>Realm</cite>
+ proposal. The following term is defined there, and used in this specification: <ref
+ spec=JSREALMS></p>
+
+ <ul class="brief">
+ <li>The <dfn data-x="js-HostInitializeUserRealm" data-x-href="https://rawgit.com/tc39/proposal-realms/master/index.html#sec-host-initialize-user-realm">HostInitializeUserRealm</dfn> abstract operation</li>
+ </ul>
+
  <p>Users agents that support JavaScript must also implement <cite>ECMAScript
  Internationalization API</cite>. <ref spec=JSINTL></p>
  </dd>
@@ -92107,6 +92115,113 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
 
  </ol>
 
+ <h5><dfn data-x="the-hostinitializeuserrealm-implementation">HostInitializeUserRealm</dfn>(<var>realm</var>)</h5>
+
+ <p>JavaScript contains an implementation-defined <span
+ data-x="js-HostInitializeUserRealm">HostInitializeUserRealm</span>(<var>realm</var>) abstract
+ operation. User agents must use the following implementation:
+ <ref spec=JAVASCRIPT>
+
+ <ol>
+
+ <li><p>Let <var>parent settings object</var> be the <span>current settings object</span>.</p></li>
+
+ <li><p>Let <var>module map</var> be a new <span>module map</span>, initially empty.</p></li>
+
+ <li>
+ <p>Let <var>settings object</var> be a new <span>environment settings object</span> whose
+ algorithms are defined as follows:</p>
+
+ <dl>
+
+ <dt>The <span>realm execution context</span></dt>
+ <dd>
+
+ <p>Return <var>realm</var>.[[ExecutionContext]].</p>
+
+ </dd>
+
+ <dt>The <span data-x="concept-settings-object-module-map">module map</span></dt>
+ <dd>
+
+ <p>Return <var>module map</var>.</p>
+
+ </dd>
+
+ <dt>The <span>responsible browsing context</span></dt>
+ <dd>
+
+ <p>Return <var>parent settings object</var>'s <span>responsible browsing context</span>.</p>
+
+ </dd>
+
+ <dt>The <span>responsible event loop</span></dt>
+ <dd>
+
+ <p>Return <var>parent settings object</var>'s <span>responsible event loop</span>.</p>
+
+ </dd>
+
+ <dt>The <span>responsible document</span></dt>
+ <dd>
+
+ <p>Return <var>parent settings object</var>'s <span>responsible document</span>.</p>
+
+ </dd>
+
+ <dt>The <span>API URL character encoding</span></dt>
+ <dd>
+
+ <p>Return <var>parent settings object</var>'s <span>API URL character encoding</span>.</p>
+
+ </dd>
+
+ <dt>The <span>API base URL</span></dt>
+ <dd>
+
+ <p>Return <var>parent settings object</var>'s <span>API base URL</span>.</p>
+
+ </dd>
+
+ <dt>The <span data-x="concept-settings-object-origin">origin</span></dt>
+ <dd>
+
+ <p>Return <var>parent settings object</var>'s <span data-x="concept-settings-object-origin">origin</span>.</p>
+
+ </dd>
+
+ <dt>The <span>HTTPS state</span></dt>
+ <dd>
+
+ <p>Return <var>parent settings object</var>'s <span>HTTPS state</span>.</p>
+
+ </dd>
+
+ <dt>The <span data-x="concept-settings-object-referrer-policy">referrer policy</span></dt>
+ <dd>
+
+ <p>Return <var>parent settings object</var>'s <span data-x="concept-settings-object-referrer-policy">referrer policy</span>.</p>
+
+ </dd>
+
+ </dl>
+ </li>
+
+ <li><p>Set <var>settings object</var>'s <span data-x="concept-environment-id">id</span> to a new
+ unique opaque string, <var>settings object</var>'s <span
+ data-x="concept-environment-creation-url">creation URL</span> to <var>parent settings
+ object</var>'s <span data-x="concept-environment-creation-url">creation URL</span>, <var>settings
+ object</var>'s <span data-x="concept-environment-target-browsing-context">target browsing
+ context</span> to <var>parent settings object</var>'s <span
+ data-x="concept-environment-target-browsing-context">target browsing context</span>, and
+ <var>settings object</var>'s <span data-x="concept-environment-active-service-worker">active
+ service worker</span> to <var>parent settings object</var>'s <span
+ data-x="concept-environment-active-service-worker">active service worker</span>.</p></li>
+
+ <li><p>Set <var>realm</var>'s [[HostDefined]] field to <var>settings object</var>.</p></li>
+
+ </ol>
+
  </div>
 
  <h4>Event loops</h4> <!-- <dfn>event loop</dfn> -->
@@ -124875,6 +124990,9 @@ INSERT INTERFACES HERE
  <dt id="refsJSON">[JSON]</dt>
  <dd><cite><a href="https://tools.ietf.org/html/rfc7159">The JavaScript Object Notation (JSON) Data Interchange Format</a></cite>, T. Bray. IETF.</dd>
 
+ <dt id="refsJSREALMS">[JSREALMS]</dt>
+ <dd><cite><a href="https://rawgit.com/tc39/proposal-realms/master/index.html">Realms</a></cite>. Ecma International.</dd>
+
  <dt id="refsLONGTASKS">[LONGTASKS]</dt>
  <dd><cite><a href="https://w3c.github.io/longtasks/">Long Tasks</a></cite>, D. Denicola, I. Grigorik, S. Panicker. W3C.</dd>