Handle module resolution when there is no active script

Closes #3295.

source

@@ -88480,20 +88480,48 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
   implementation: <ref spec=JAVASCRIPT> <ref spec=JSIMPORT></p>
 
   <ol>
-   <li><p>Let <var>referencing script</var> be
-   <var>referencingScriptOrModule</var>.[[HostDefined]].</p></li>
+   <li><p>Let <var>settings object</var> be the <span>current settings object</span>.</p></li>
 
-   <li><p>Let <var>moduleMap</var> be <var>referencing script</var>'s <span>settings object</span>'s
-   <span data-x="concept-settings-object-module-map">module map</span>.</p></li>
+   <li><p>Let <var>base URL</var> be <var>settings object</var>'s <span>API base
+   URL</span>.</p></li>
+
+   <li>
+    <p>If <var>referencingScriptOrModule</var> is not null, then:</p>
+
+    <ol>
+     <li><p>Let <var>referencing script</var> be
+     <var>referencingScriptOrModule</var>.[[HostDefined]].</p></li>
+
+     <li><p>Set <var>settings object</var> to <var>referencing script</var>'s <span>settings
+     object</span>.</p></li>
+
+     <li><p>Set <var>base URL</var> to <var>referencing script</var>'s <span
+     data-x="concept-script-base-url">base URL</span>.</p></li>
+    </ol>
+
+    <div class="example">
+     <p><var>referencingScriptOrModule</var> is not usually null. One case where it <em>can</em> be
+     null is if the user clicks the control in the following example:</p>
+
+     <pre><code class="html" data-x="">&lt;button onclick="import('./foo.mjs')">Click me&lt;/button></code></pre>
+
+     <p>In this case, at the time the <code>import()</code> expression runs,
+     <span>GetActiveScriptOrModule</span> will return null, which will be passed to this abstract
+     operation when <span data-x="js-HostResolveImportedModule">HostResolveImportedModule</span> is
+     called by <span>FinishDynamicImport</span>.</p>
+    </div>
+   </li>
+
+   <li><p>Let <var>moduleMap</var> be <var>settings object</var>'s <span
+   data-x="concept-settings-object-module-map">module map</span>.</p></li>
 
    <li><p>Let <var>url</var> be the result of <span data-x="resolve a module specifier">resolving a
-   module specifier</span> given <var>referencing script</var>'s <span
-   data-x="concept-script-base-url">base URL</span> and <var>specifier</var>.</p></li>
+   module specifier</span> given <var>base URL</var> and <var>specifier</var>.</p></li>
 
    <li><p>Assert: <var>url</var> is never failure, because <span data-x="resolve a module
-   specifier">resolving a module specifier</span> must have been <a
-   href="#validate-requested-module-specifiers">previously successful</a> with these
-   same two arguments.</p></li>
+   specifier">resolving a module specifier</span> must have been previously successful with these
+   same two arguments (either <a href="#validate-requested-module-specifiers">while creating the
+   corresponding module script</a>, or in <span>HostImportModuleDynamically</span>).</p></li>
 
    <li><p>Let <var>resolved module script</var> be <var>moduleMap</var>[<var>url</var>]. (This entry
    must <span data-x="map exists">exist</span> for us to have gotten to this point.)</p></li>
@@ -88516,16 +88544,42 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
   User agents must use the following implementation: <ref spec=JSIMPORT></p>
 
   <ol>
-   <li><p>Let <var>referencing script</var> be
-   <var>referencingScriptOrModule</var>.[[HostDefined]].</p></li>
+   <li><p>Let <var>settings object</var> be the <span>current settings object</span>.</p></li>
+
+   <li><p>Let <var>base URL</var> be <var>settings object</var>'s <span>API base
+   URL</span>.</p></li>
+
+   <li><p>Let <var>fetch options</var> be the <span>default classic script fetch
+   options</span>.</p></li>
+
+   <li>
+    <p>If <var>referencingScriptOrModule</var> is not null, then:</p>
+
+    <ol>
+     <li><p>Let <var>referencing script</var> be
+     <var>referencingScriptOrModule</var>.[[HostDefined]].</p>
+
+     <li><p>Set <var>settings object</var> to <var>referencing script</var>'s <span>settings
+     object</span>.</p></li>
+
+     <li><p>Set <var>base URL</var> to <var>referencing script</var>'s <span
+     data-x="concept-script-base-url">base URL</span>.</p></li>
+
+     <li><p>Set <var>fetch options</var> to the <span>descendant script fetch options</span> for
+     <var>referencing script</var>'s <span data-x="concept-script-script-fetch-options">fetch
+     options</span>.</p></li>
+    </ol>
+
+    <p class="note">As explained above for <span>HostResolveImportedModule</span>, in the common
+    case, <var>referencingScriptOrModule</var> is non-null.</p>
+   </li>
 
    <li>
     <p>Run the following steps <span>in parallel</span>:</p>
 
     <ol>
      <li><p>Let <var>url</var> be the result of <span data-x="resolve a module specifier">resolving a
-     module specifier</span> given <var>referencing script</var>'s <span
-     data-x="concept-script-base-url">base URL</span> and <var>specifier</var>.</p></li>
+     module specifier</span> given <var>base URL</var> and <var>specifier</var>.</p></li>
 
      <li>
       <p>If <var>url</var> is failure, then:</p>
@@ -88541,14 +88595,9 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
       </ol>
      </li>
 
-     <li><p>Let <var>options</var> be the <span>descendant script fetch options</span> for
-     <var>referencing script</var>'s <span data-x="concept-script-script-fetch-options">fetch
-     options</span>.</p></li>
-
-     <li><p><span>Fetch a module script graph</span> given <var>url</var>, <var>referencing
-     script</var>'s <span>settings object</span>, "<code data-x="">script</code>", and
-     <var>options</var>. Wait until the algorithm asynchronously completes with
-     <var>result</var>.</p></li>
+     <li><p><span>Fetch a module script graph</span> given <var>url</var>, <var>settings
+     object</var>, "<code data-x="">script</code>", and <var>fetch options</var>. Wait until the
+     algorithm asynchronously completes with <var>result</var>.</p></li>
 
      <li>
       <p>If <var>result</var> is null, then:</p>