Support chrome-extension:// scheme in URLPattern.

chrome/common/extensions/docs/static/match_patterns.html

 <div id="pageData-name" class="pageData">Match Patterns</div>
 
 <p>
 <a href="content_scripts.html">Content scripts</a> operate on
 a set of URLs defined by match patterns.
 You can put one or more match patterns
 in the <code>"matches"</code> part of
 a content script's section of the manifest,
 as well as in the <code>"exclude_matches"</code> section.
 This page describes the match pattern syntax &mdash;
 the rules you need to follow when you specify
 which URLs your content script affects.
 </p>
 
 <p>
 A match pattern is essentially a URL
 that begins with a permitted scheme (<code>http</code>,
-<code>https</code>, <code>file</code>, or <code>ftp</code>),
+<code>https</code>, <code>file</code>, <code>ftp</code>, or
+<code>chrome-extension</code>),
 and that can contain '<code>*</code>' characters.
 The special pattern
 <code>&lt;all_urls&gt;</code> matches any URL
 that starts with a permitted scheme.
 Each match pattern has 3 parts:</p>
 </p>
 
 <ul>
   <li> <em>scheme</em> &mdash;
     for example, <code>http</code> or <code>file</code>
@@ skipping 15 matching lines @@
   <li> <em>path</em> &mdash;
     for example, <code>/*</code>, <code>/foo* </code>,
     or <code>/foo/bar </code>
   </li>
 </ul>
 
 <p>Here's the basic syntax:</p>
 
 <pre>
 <em>&lt;url-pattern&gt;</em> := <em>&lt;scheme&gt;</em>://<em>&lt;host&gt;</em><em>&lt;path&gt;</em>
-<em>&lt;scheme&gt;</em> := '*' | 'http' | 'https' | 'file' | 'ftp'
+<em>&lt;scheme&gt;</em> := '*' | 'http' | 'https' | 'file' | 'ftp' | 'chrome-extension'
 <em>&lt;host&gt;</em> := '*' | '*.' <em>&lt;any char except '/' and '*'&gt;</em>+
 <em>&lt;path&gt;</em> := '/' <em>&lt;any chars&gt;</em>
 </pre>
 
 <p>
 The meaning of '<code>*</code>' depends on whether
 it's in the <em>scheme</em>, <em>host</em>, or <em>path</em> part.
 If the <em>scheme</em> is <code>*</code>,
 then it matches either <code>http</code> or <code>https</code>.
 If the <em>host</em> is just <code>*</code>,
@@ skipping 114 matching lines @@
   </td>
 
   <td>
     http://mail.google.com/foo/baz/bar<br>
     https://mail.google.com/foobar
   </td>
 </tr>
 
 <tr>
   <td>
+    <code>chrome-extension://*/* </code>
+  </td>
+
+  <td>
+    Matches any URL pointing to an extension (the first <code>*</code>
+    represents a filter for extension IDs, the second for paths).
+  </td>
+
+  <td>
+    chrome-extension://askla...asdf/options.html
+  </td>
+</tr>
+
+<tr>
+  <td>
     <code>&lt;all_urls&gt;</code>
   </td>
 
   <td>
     Matches any URL that uses a permitted scheme.
     (See the beginning of this section for the list of permitted
     schemes.)
   </td>
   <td>
     http://example.org/foo/bar.html<br>
@@ skipping 33 matching lines @@
   <td><code>http:/bar</code></td>
   <td>Missing <em>scheme</em> separator ("/" should be "//")</td>
 </tr>
 
 <tr>
   <td><code>foo://*</code></td>
   <td>Invalid <em>scheme</em></td>
 </tr>
 </tbody>
 </table>
+
+<p>
+Some schemes are not supported in all contexts.
+</p>