[fsp] Add support for opening files.

chrome/common/extensions/api/file_system_provider_internal.idl

 // Copyright 2014 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.
 
 // Internal, used by fileSystemProvider's custom bindings. These functions are
 // called when events' callbacks are invoked.
 [platforms=("chromeos"),
  implemented_in="chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.h", nodoc]
 namespace fileSystemProviderInternal {
   interface Functions {
@@ skipping 30 matching lines @@
         long requestId,
         fileSystemProvider.EntryMetadata[] entries,
         boolean hasNext);
 
     // Internal. Error callback of the <code>onReadDirectoryRequested</code>
     // event. Must be called when reading a directory fails.
     static void readDirectoryRequestedError(
         long fileSystemId,
         long requestId,
         fileSystemProvider.ProviderError error);
+
+    // Internal. Success callback of the <code>onOpenFileRequested</code> event.
+    // Must be called, when opening succeeds.
+    static void openFileRequestedSuccess(
+        long fileSystemId,
+        long requestId);
+
+    // Internal. Error callback of the <code>onOpenFileRequested</code> event.
+    // Must be called when opening fails.
+    static void openFileRequestedError(
+        long fileSystemId,
+        long requestId,
+        fileSystemProvider.ProviderError error);
   };
 };