Convert the utility process image decoder into a Mojo service.

chrome/browser/image_decoder.h

 // 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.
 
 #ifndef CHROME_BROWSER_IMAGE_DECODER_H_
 #define CHROME_BROWSER_IMAGE_DECODER_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/sequence_checker.h"
 #include "base/sequenced_task_runner.h"
 #include "base/synchronization/lock.h"
 #include "base/timer/timer.h"
 #include "build/build_config.h"
 #include "content/public/browser/utility_process_host.h"
 #include "content/public/browser/utility_process_host_client.h"
 
 class SkBitmap;
 
+namespace mojom {
+class ImageDecoder;
+}
+
+namespace mojo {
+template <typename T> class InterfacePtr;
+}
+
 // This is a helper class for decoding images safely in a utility process. To
 // use this, call ImageDecoder::Start(...) or
 // ImageDecoder::StartWithOptions(...) on any thread.
 //
 // Internally, most of the work happens on the IO thread, and then
 // the callback (ImageRequest::OnImageDecoded or
 // ImageRequest::OnDecodeImageFailed) is posted back to the |task_runner_|
 // associated with the ImageRequest.
 // The Cancel() method runs on whichever thread called it. |map_lock_| is used
 // to protect the data that is accessed from multiple threads.
@@ skipping 113 matching lines @@
   // Protects |image_request_id_map_| and |image_request_id_counter_|.
   base::Lock map_lock_;
 
   // The UtilityProcessHost requests are sent to.
   base::WeakPtr<content::UtilityProcessHost> utility_process_host_;
 
   // Calls StopBatchMode() after |kBatchModeTimeoutSeconds| have elapsed,
   // unless a new decoding request resets the timer.
   scoped_ptr<base::DelayTimer> batch_mode_timer_;
 
+  // Mojo service connection. Must always be bound/reset and used on the IO
+  // thread.
+  scoped_ptr<mojo::InterfacePtr<mojom::ImageDecoder>> decoder_;

[jam, 2016/03/31 17:46:33]

why is this in a scoped ptr instead of having the raw interfaceptr as we usually
do? 

[Anand Mistry (off Chromium), 2016/04/01 05:35:11]

Oops. Artifact of the previous (in components) incarnation where I wanted to
avoid exposing mojo. Not necessary any more.

+
   DISALLOW_COPY_AND_ASSIGN(ImageDecoder);
 };
 
 #endif  // CHROME_BROWSER_IMAGE_DECODER_H_