[fsp] Add requestUnmount() method together with the request manager.

chrome/test/data/extensions/api_test/file_system_provider/mount/test.js

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 chrome.test.runTests([
+  // Tests whether mounting succeeds, when a non-empty name is provided.
   function goodDisplayName() {
     chrome.fileSystemProvider.mount(
       'test file system',
       function(fileSystemId) {
         chrome.test.assertEq('number', typeof(fileSystemId));
         chrome.test.assertTrue(fileSystemId == 1);
         chrome.test.succeed();
       },
       function(error) {
         chrome.test.fail();
       }
     );
   },
 
+  // Verifies that mounting fails, when an empty string is provided as a name.
   function emptyDisplayName() {
     chrome.fileSystemProvider.mount(
       '',
       function(fileSystemId) {
         chrome.test.fail();
       },
       function(error) {
         chrome.test.assertEq('SecurityError', error.name);
         chrome.test.succeed();
       }
     );
   },
 
+  // End to end test. Mounts a volume using fileSystemProvider.mount(), then
+  // checks if the mounted volume is added to VolumeManager, by querying
+  // fileBrowserPrivate.getVolumeMetadataList().
   function successfulMount() {
     chrome.fileSystemProvider.mount(
       'caramel-candy.zip',
       function(fileSystemId) {
           chrome.test.assertTrue(fileSystemId > 0);
         chrome.fileBrowserPrivate.getVolumeMetadataList(function(volumeList) {
           var found = volumeList.filter(function(volumeInfo) {
             return volumeInfo.volumeId ==
                 'provided:' + chrome.runtime.id + '-' + fileSystemId + '-user';
           });
           chrome.test.assertEq(1, found.length);
           chrome.test.succeed();
         });
       },
       function(error) {
         chrome.test.fail();
       });
   },
 
+  // Checks is limit for mounted file systems per profile works correctly.
+  // Tries to create more than allowed number of file systems. All of the mount
+  // requests should succeed, except the last one which should fail with a
+  // security error.
   function stressMountTest() {
-    // Try to create more than allowed number of file systems. All of the mount
-    // requests should succeed, except the last one which should fail with a
-    // security error.
     var ALREADY_MOUNTED_FILE_SYSTEMS = 2;  // By previous tests.
     var MAX_FILE_SYSTEMS = 16;
     var index = 0;
     var tryNextOne = function() {
       index++;
       if (index < MAX_FILE_SYSTEMS - ALREADY_MOUNTED_FILE_SYSTEMS + 1) {
         chrome.fileSystemProvider.mount(
             index + 'th file system',
             function(fileSystemId) {
               chrome.test.assertTrue(fileSystemId > 0);
               tryNextOne();
             },
             chrome.test.fail);
       } else {
         chrome.fileSystemProvider.mount(
             'over the limit fs',
             chrome.test.fail,
             function(error) {
               chrome.test.assertEq('SecurityError', error.name);
               chrome.test.succeed();
             });
       }
     };
     tryNextOne();
   }
 ]);