Implement Worker-MainThread bridge for FileSystem API in Chrome

content/child/fileapi/file_system_dispatcher.h

Index: content/child/fileapi/file_system_dispatcher.h
diff --git a/content/child/fileapi/file_system_dispatcher.h b/content/child/fileapi/file_system_dispatcher.h
index a8fc624a059725561130343be8369735fee2a6b7..c994a6c39a11a4d713c0df61f5d53bf85388096b 100644
--- a/content/child/fileapi/file_system_dispatcher.h
+++ b/content/child/fileapi/file_system_dispatcher.h
@@ -40,7 +40,8 @@ class FileSystemDispatcher : public IPC::Listener {
       const base::PlatformFileInfo& file_info)> MetadataCallback;
   typedef base::Callback<void(
       const base::PlatformFileInfo& file_info,
-      const base::FilePath& platform_path)> CreateSnapshotFileCallback;
+      const base::FilePath& platform_path,
+      int request_id)> CreateSnapshotFileCallback;
   typedef base::Callback<void(
       const std::vector<fileapi::DirectoryEntry>& entries,
       bool has_more)> ReadDirectoryCallback;
@@ -122,6 +123,9 @@ class FileSystemDispatcher : public IPC::Listener {
   // raw PlatformFile returned from OpenFile.
   void NotifyCloseFile(int file_open_id);
 
+  // The caller must send FileSystemHostMsg_DidReceiveSnapshot message
+  // with |request_id| passed to |success_callback| after the snapshot file
+  // is successfully received.
   void CreateSnapshotFile(const GURL& file_path,
                           const CreateSnapshotFileCallback& success_callback,
                           const StatusCallback& error_callback);