Fix filesystem API file_handlers to work for drive on ChromeOS.

chrome/browser/chromeos/drive/drive_file_system_proxy.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/chromeos/drive/drive_file_system_proxy.h"
 
 #include <string>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 679 matching lines @@
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 }
 
 // static.
 bool DriveFileSystemProxy::ValidateUrl(
     const FileSystemURL& url, base::FilePath* file_path) {
   // what platform you're on.
   if (!url.is_valid() || url.type() != fileapi::kFileSystemTypeDrive) {
     return false;
   }
-  *file_path = url.virtual_path();
-  return true;
+
+  // |url.virtual_path()| cannot be used directly because in the case the url is
+  // isolated file system url, the virtual path will be formatted as
+  // <isolated_file_system_id>/<file_name> and thus unusable by drive file
+  // system.
+  // TODO(kinaba): fix other uses of virtual_path() as in
+  // https://codereview.chromium.org/12483010/
+  *file_path = util::ExtractDrivePath(url.path());
+  return !file_path->empty();
 }
 
 void DriveFileSystemProxy::CallDriveFileSystemMethodOnUIThread(
     const base::Closure& method_call) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   BrowserThread::PostTask(
       BrowserThread::UI,
       FROM_HERE,
       base::Bind(
           &DriveFileSystemProxy::CallDriveFileSystemMethodOnUIThreadInternal,
@@ skipping 98 matching lines @@
   CallDriveFileSystemMethodOnUIThread(
       base::Bind(&DriveFileSystemInterface::CloseFile,
                  base::Unretained(file_system_),
                  virtual_path,
                  google_apis::CreateRelayCallback(
                      base::Bind(&EmitDebugLogForCloseFile,
                                 virtual_path))));
 }
 
 }  // namespace drive