Created a helper function "FindDiskBySourcePath" in DiskMountManager.

chrome/browser/chromeos/disks/disk_mount_manager.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/disks/disk_mount_manager.h"
 
 #include <sys/statvfs.h>
 
 #include <map>
 #include <set>
@@ skipping 212 matching lines @@
     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
     cros_disks_client_->EnumerateAutoMountableDevices(
         base::Bind(&DiskMountManagerImpl::OnRequestMountInfo,
                    weak_ptr_factory_.GetWeakPtr()),
         base::Bind(&base::DoNothing));
   }
 
   // DiskMountManager override.
   const DiskMap& disks() const OVERRIDE { return disks_; }
 
+  // DiskMountManager override.
+  virtual const Disk* FindDiskBySourcePath(const std::string& source_path)
+      const OVERRIDE {
+    DiskMap::const_iterator disk_it = disks_.find(source_path);
+    return disk_it == disks_.end() ? NULL : disk_it->second;
+  }
 
   // DiskMountManager override.
   const MountPointMap& mount_points() const OVERRIDE { return mount_points_; }
 
  private:
   struct UnmountDeviceRecursiveCallbackData {
     void* user_data;
     UnmountDeviceRecursiveCallbackType callback;
     size_t pending_callbacks_count;
 
@@ skipping 448 matching lines @@
   VLOG(1) << "DiskMountManager Shutdown completed";
 }
 
 // static
 DiskMountManager* DiskMountManager::GetInstance() {
   return g_disk_mount_manager;
 }
 
 }  // namespace disks
 }  // namespace chromeos