[fsp] Add support for truncating files.

chrome/common/extensions/api/file_system_provider.idl

 // 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.
 
 // Use the <code>chrome.fileSystemProvider</code> API to create file systems,
 // that can be accessible from the file manager on Chrome OS.
 [platforms=("chromeos"),
  implemented_in="chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.h"]
 namespace fileSystemProvider {
   // Error codes used by providing extensions in response to requests. For
@@ skipping 131 matching lines @@
   };
 
   // Options for the <code>onMoveEntryRequested()</code> event.
   dictionary MoveEntryRequestedOptions {
     DOMString fileSystemId;
     long requestId;
     DOMString sourcePath;
     DOMString targetPath;
   };
 
+  // Options for the <code>onTruncateRequested()</code> event.
+  dictionary TruncateRequestedOptions {
+    DOMString fileSystemId;
+    long requestId;
+    DOMString filePath;
+    double length;
+  };
+
   // Callback to receive the result of mount() function.
   callback MountCallback = void([nodoc, instanceOf=DOMError] object error);
 
   // Callback to receive the result of unmount() function.
   callback UnmountCallback = void([nodoc, instanceOf=DOMError] object error);
 
   // Callback to handle an error raised from the browser.
   [nocompile] callback ErrorCallback = void([instanceOf=DOMError] object error);
 
   // Callback to be called by the providing extension in case of a success.
@@ skipping 127 matching lines @@
         CopyEntryRequestedOptions options,
         ProviderSuccessCallback successCallback,
         ProviderErrorCallback errorCallback);
 
     // Raised when moving an entry (recursively if a directory) is requested.
     // If an error occurs, then <code>errorCallback</code> must be called.
     [maxListeners=1, nodoc] static void onMoveEntryRequested(
         MoveEntryRequestedOptions options,
         ProviderSuccessCallback successCallback,
         ProviderErrorCallback errorCallback);
+
+    // Raised when truncating a file to a desired length is requested.
+    // If an error occurs, then <code>errorCallback</code> must be called.
+    [maxListeners=1, nodoc] static void onTruncateRequested(
+        TruncateRequestedOptions options,
+        ProviderSuccessCallback successCallback,
+        ProviderErrorCallback errorCallback);
   };
 };