Allow content script insertion on about:-URLs.

chrome/common/extensions/docs/templates/articles/content_scripts.html

 <h1>Content Scripts</h1>
 
 
 <p>
 Content scripts are JavaScript files that run in the context of web pages.
 By using the standard
 <a href="http://www.w3.org/TR/DOM-Level-2-HTML/">Document
 Object Model</a> (DOM),
 they can read details of the web pages the browser visits,
 or make changes to them.
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     <td>array of strings</td>
     <td><em>Optional.</em>
     Excludes pages that this content script would otherwise be
     injected into.
     See <a href="match_patterns.html">Match Patterns</a>
     for more details on the syntax of these strings
     and <a href="#match-patterns-globs">Match patterns and globs</a>
     for information on how to exclude URLs.</td>
   </tr>
   <tr>
+    <td><code>match_about_blank<code></td>
+    <td>boolean</td>
+    <td><em>Optional.</em>
+    Whether to insert the content script on <code>about:blank</code> and
+    <code>about:srcdoc</code>. Content scripts will only be injected on pages if
+    your extension has access to the page's parent document. Scripts are only
+    inserted in a top-level <code>about:blank</code> frame when its opener is
+    accessible by the extension.
+    <br><br>
+    Defaults to <code>false</code>.</td>
+  </tr>
+  <tr>
     <td><code>css<code></td>
     <td>array of strings</td>
     <td><em>Optional.</em>
     The list of CSS files to be injected into matching pages. These are injected in the order they appear in this array, before any DOM is constructed or displayed for the page.</td>
   </tr>
   <tr>
     <td><code>js<code></td>
     <td><nobr>array of strings</nobr></td>
     <td><em>Optional.</em>
     The list of JavaScript files to be injected into matching pages. These are injected in the order they appear in this array.</td>
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 <p>
 The next video describes message passing,
 featuring an example of a content script
 sending a request to its parent extension.
 </p>
 
 <p>
 <iframe title="YouTube video player" width="640" height="390" src="//www.youtube.com/embed/B4M_a7xejYI?rel=0" frameborder="0" allowfullscreen></iframe>
 </p>