[WIP] Top-level await integration

The purpose of this patch is to nail down how HTML would
adjust to the needs of top-level await. The relevant change is,
the module.Evaluate() method will return a Promise that resolves
when the module is ready, and this will be passed to
FinishDynamicImport to wait on before resolving the Promise it returns.
It doesn't seem like anyone else needs to wait for a module script
to "finish" evaluating besides dynamic import.

This PR is just a sketch, not to be landed. Top-level await should
reach stage 3 before this change lands.

The PR where Evaluate returns a Promise is
guybedford/proposal-top-level-await#1

Author: littledan

source

@@ -87761,12 +87761,9 @@ interface <dfn>ApplicationCache</dfn> : <span>EventTarget</span> {
 
    <li><p><span>Prepare to run script</span> given <var>settings</var>.</p></li>
 
-   <li><p>Let <var>evaluationStatus</var> be null.</p></li>
-
    <li><p>If <var>script</var>'s <span data-x="concept-script-error-to-rethrow">error to
-   rethrow</span> is not null, then set <var>evaluationStatus</var> to Completion { [[Type]]: throw,
-   [[Value]]: <var>script</var>'s <span data-x="concept-script-error-to-rethrow">error to
-   rethrow</span>, [[Target]]: empty }.</p></li>
+   rethrow</span> is not null, then let <var>evaluationPromise</var> be a promise rejected with <var>script</var>'s <span data-x="concept-script-error-to-rethrow">error to
+   rethrow</span>.</p></li>
 
    <li>
     <p>Otherwise:</p>
@@ -87776,35 +87773,26 @@ interface <dfn>ApplicationCache</dfn> : <span>EventTarget</span> {
      data-x="concept-script-record">record</span>.</p>
 
      <li>
-      <p>Set <var>evaluationStatus</var> to <var>record</var>.<span
+      <p>Let <var>evaluationPromise</var> be <var>record</var>.<span
       data-x="js-Evaluate">Evaluate</span>().</p>
 
       <p class="note">This step will recursively evaluate all of the module's dependencies.</p>
 
       <p>If <span data-x="js-Evaluate">Evaluate</span> fails to complete as a result of the user agent
-      <span data-x="abort a running script">aborting the running script</span>, then set
-      <var>evaluationStatus</var> to Completion { [[Type]]: throw, [[Value]]: a new
-      <span>"<code>QuotaExceededError</code>"</span> <code>DOMException</code>, [[Target]]: empty
-      }.</p>
+      <span data-x="abort a running script">aborting the running script</span>, then let
+      <var>evaluationPromise</var> be a promise rejected with a new
+      <span>"<code>QuotaExceededError</code>"</span> <code>DOMException</code>.</p>
       </li>
     </ol>
    </li>
 
-   <li>
-    <p>If <var>evaluationStatus</var> is an <span>abrupt completion</span>, then:</p>
-
-    <ol>
-     <li><p>If <var>rethrow errors</var> is true, rethrow the exception given by
-     <var>evaluationStatus</var>.[[Value]].</p></li>
-
-     <li><p>Otherwise, <span>report the exception</span> given by
+   <li><p>If <var>rethrow errors</var> is false, then upon rejection of
+     <var>evaluationPromise</var>, <span>report the exception</span> given by
      <var>evaluationStatus</var>.[[Value]] for <var>script</var>.</p></li>
-    </ol>
-   </li>
 
    <li><p><span>Clean up after running script</span> with <var>settings</var>.</p></li>
 
-   <li><p>Return <var>evaluationStatus</var>.</p></li>
+   <li><p>Return <var>evaluationPromise</var>.</p></li>
   </ol>
 
   <p>The steps to <dfn>check if we can run script</dfn> with an <span>environment settings
@@ -88882,11 +88870,10 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
     <p>If <var>url</var> is failure, then:</p>
 
     <ol>
-     <li><p>Let <var>completion</var> be Completion { [[Type]]: throw, [[Value]]: a new
-     <code>TypeError</code>, [[Target]]: empty }.</p></li>
+     <li><p>Let <var>promise</var> be a promise rejected with a new <code>TypeError</code>.</p></li>
 
      <li><p>Perform <span>FinishDynamicImport</span>(<var>referencingScriptOrModule</var>,
-     <var>specifier</var>, <var>promiseCapability</var>, <var>completion</var>).</p></li>
+     <var>specifier</var>, <var>promiseCapability</var>, <var>promise</var>).</p></li>
 
      <li><p>Return.</p></li>
     </ol>
@@ -88900,28 +88887,23 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
     <p>If <var>result</var> is null, then:</p>
 
     <ol>
-     <li><p>Let <var>completion</var> be Completion { [[Type]]: throw, [[Value]]: a new
-     <code>TypeError</code>, [[Target]]: empty }.</p></li>
+     <li><p>Let <var>promise</var> be a promise rejected with a new <code>TypeError</code>.</p></li>
 
      <li><p>Perform <span>FinishDynamicImport</span>(<var>referencingScriptOrModule</var>,
-     <var>specifier</var>, <var>promiseCapability</var>, <var>completion</var>).</p></li>
+     <var>specifier</var>, <var>promiseCapability</var>, <var>promise</var>).</p></li>
 
      <li><p>Return.</p></li>
     </ol>
    </li>
 
    <li><p><span data-x="run a module script">Run the module script</span> <var>result</var>, with
-   the rethrow errors boolean set to true.</p></li>
+   the rethrow errors boolean set to true, and let the result be <var>promise</var>.</p></li>
 
-   <li><p>If running the module script throws an exception, then perform
+   <li><p>Perform
    <span>FinishDynamicImport</span>(<var>referencingScriptOrModule</var>, <var>specifier</var>,
-   <var>promiseCapability</var>, the thrown exception completion).</p></li>
+   <var>promiseCapability</var>, <var>promise</var>).</p></li>
 
-   <li><p>Otherwise, perform
-   <span>FinishDynamicImport</span>(<var>referencingScriptOrModule</var>, <var>specifier</var>,
-   <var>promiseCapability</var>, <span>NormalCompletion</span>(undefined)).</p></li>
-
-   <li><p>Return undefined.</p></li>
+   <li><p>Return.</p></li>
   </ol>
 
   <h6