Media Galleries: Disable write support.

chrome/common/extensions/docs/templates/intros/mediaGalleries.html

 <table class="intro">
   <tr>
     <th scope="col"></th>
     <th scope="col"></th>
   </tr>
   <tr>
     <td><strong>Description:</strong></td>
     <td>Use the <code>chrome.mediaGalleries</code> API
     to access media files (images, video, audio)
     from the user's local disks (with the user's consent).</td>
   </tr>
   <tr>
     <td><strong>Availability:</strong></td>
-    <td>Google Chrome 23 (read permission)<br>
-    Google Chrome 26 (write permission)</td>
+    <td>Google Chrome 23 (read permission)</td>
   </tr>
   <tr>
     <td><strong>Permissions:</strong></td>
-    <td><code>"mediaGalleries": ["accessType"]</code>,
-    <code>"mediaGalleries": ["accessType", "allAutoDetected"]</code><br>
+    <td><code>"mediaGalleries": ["read"]</code>,
+    <code>"mediaGalleries": ["read", "allAutoDetected"]</code><br>
     See <a href="#manifest">Manifest</a> below
     for more information.</td>
   </tr>
   <tr>
     <td><strong>Learn more:</strong></td>
     <td><a href="https://developers.google.com/live/shows/10479832/">Chrome Office Hours: The Media Galleries API</a></td>
   </tr>
 </table>
 
 <h2 id="usage">Usage</h2>
@@ skipping 28 matching lines @@
 
 <pre>{
   "name": "My extension",
   ...
   "permissions": [
     <b>{ "mediaGalleries": ["read", "allAutoDetected"] }</b>
   ],
   ...
 }</pre>
 
-<p>The above permission will trigger an install time permission prompt
+<p>This permission will trigger an install time permission prompt
 and let the extension read from all auto-detected media galleries on the
 user's computer. The user may add or remove galleries using the
 media gallery management dialog, after which the extension will be able
 to read all the media files from galleries that the user has selected.</p>
 
-<p>Another possible access type is "write", which can be put in place of
-"read". Specifying "write" allows read and write access to the accessible
-media galleries.
-</p>
-
-<p>Currently "read" and "write" access types are supported by
-this API. Add-file access with be implemented soon.</p>
+<p>Currently "read" is the only access type supported by
+this API. Read-write and add-file access with be implemented soon.</p>