Add events for configuring and adding new providers to FSP API.

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

 <h2 id="manifest">Manifest</h2>
 <p>You must declare the "fileSystemProvider" permission
 in the <a href="manifest">extension manifest</a>
 to use the File System Provider API.
 For example:</p>
 <pre data-filename="manifest.json">
 {
   "name": "My extension",
   ...
   <b>"permissions": [
     "fileSystemProvider"
   ]</b>,
   ...
 }
 </pre>
 
 <h2 id="overview">Overview</h2>
 <p>
 File System Provider API allows extensions to support virtual file systems,
 which are available in the file manager on Chrome OS.
 Use cases include decompressing archives and accessing files in a cloud
 service other than Drive.
 </p>
 
-<h2 id="archives">File handlers</h2>
+<h2 id="archives">Mounting file systems</h2>
 <p>
-Provided file systems can either provide file system contents from an external
-source (such as a remote server), or using a local file (such as an archive) as
-its input.
+Providing extensions can either provide file system contents from an external
+source (such as a remote server or a USB device), or using a local file (such as
+an archive) as its input.
 </p>
 <p>
-In the second case, the providing extension should have a
+For file handlers, the providing extension should have a
 <a href="manifest/file_handlers">file_handlers</a> manifest entry in order
 to be launched when the file is selected in the file manager.
 When the extension is executed with a file to be handled, it has to mount a
 file system and start serving contents from the provided file.
 </p>
+<p>
+If the source is network or a device, then the file system should be mounted
+when <a href="#event-onMountRequested">onMountDialogRequested</a> event is
+called.
+</p>
+<p>
+  <table>
+    <tr>
+      <th>
+        <a href="#property-options-source">Source</a> of the file system data
+      </th>
+      <th>Entry point</th>
+    </tr>
+    <tr>
+      <td>
+        <code>"FILE"</code>
+      </td>
+      <td>
+        <a href="apps/app_runtime#event-onLaunched">onLaunched</a>
+      </td>
+    </tr>
+    <tr>
+      <td>
+        <code>"DEVICE"</code>, <code>"NETWORK"</code>
+      </td>
+      <td>
+        <a href="#event-onMountRequested">onMountRequested</a>
+      </td>
+    </tr>
+  </table>
+</p>
+
+<h2 id="archives">Configuring file systems</h2>
+<p>
+Provided file systems once mounted can be configured via the
+<a href="#event-onConfigureRequested">onConfigureRequested</a> event.
+It's especially useful for file systems which provide contents via network in
+order to set proper credentials. Handling this event is optional.
+</p>
 
 <h2 id="archives">Life cycle</h2>
 <p>
 Provided file systems once mounted are remembered by Chrome and remounted
 automatically after reboot or restart. Hence, once a file system is
-<a href="method-mount">mounted</a> by a providing extension, it will stay until
+<a href="#method-mount">mounted</a> by a providing extension, it will stay until
 either the extension is unloaded, or the extension calls the
 <a href="#method-unmount"> unmount</a> method.
 </p>
 <p>
 In case of acting as a file handler, the handled file may need to be stored
 to access it after either a reboot, or suspending and resuming an event page
 of the providing extension. In such case
 <a href="fileSystem#method-retainEntry">chrome.fileSystem.retainEntry</a> and
 <a href="fileSystem#method-restoreEntry">chrome.fileSystem.restoreEntry</a>
 should be used.
 </p>