Make VideoCaptureController single-threaded and not ref counted.

content/browser/renderer_host/media/video_capture_host.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.
 //
 // VideoCaptureHost serves video capture related messages from
 // VideoCaptureMessageFilter which lives inside the render process.
 //
 // This class is owned by BrowserRenderProcessHost, and instantiated on UI
 // thread, but all other operations and method calls happen on IO thread.
 //
@@ skipping 21 matching lines @@
 //      | < VideoCaptureMsg_StateChanged      |
 //      |         (kStopped)                  |
 //      v                                     v
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_HOST_H_
 #define CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_HOST_H_
 
 #include <map>
 
 #include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
 #include "base/sequenced_task_runner_helpers.h"
 #include "content/browser/renderer_host/media/video_capture_controller.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/browser_message_filter.h"
 #include "ipc/ipc_message.h"
 
 namespace media {
 class VideoCaptureCapability;
 }
 
@@ skipping 38 matching lines @@
   virtual ~VideoCaptureHost();
 
   // IPC message: Start capture on the VideoCaptureDevice referenced by
   // VideoCaptureParams::session_id. |device_id| is an id created by
   // VideoCaptureMessageFilter to identify a session
   // between a VideoCaptureMessageFilter and a VideoCaptureHost.
   void OnStartCapture(int device_id,
                       const media::VideoCaptureParams& params);
   void OnControllerAdded(
       int device_id, const media::VideoCaptureParams& params,
-      VideoCaptureController* controller);
+      base::WeakPtr<VideoCaptureController> controller);

[Ami GONE FROM CHROMIUM, 2013/09/13 21:17:59]

I guess all these base::WeakPtr<VideoCaptureController>'s are implicitly about
the IO thread, since VCC is so IOthread-ish now.  I just wish there was a way to
annotate them as such in headers.
(nothing actionable for you here unless you can think of a way to effect this
annotation cleverly)

[ncarter (slow), 2013/09/14 00:07:24]

renamed to handler_as_controller. Just kidding; but seriously I know what you
mean. My preferred fix here is actually to stop using the VCC pointer as the
registration token altogether, the whole process by which the VCH/VCC become
mutually aware is kind of weird actually. The old code did a
make_scoped_refptr<> on a bare pointer, so I'm still counting the use of weakptr
here as a slight improvement, is how I sleep at night.

   void DoControllerAddedOnIOThread(
       int device_id, const media::VideoCaptureParams params,
-      VideoCaptureController* controller);
+      base::WeakPtr<VideoCaptureController> controller);
 
   // IPC message: Stop capture on device referenced by |device_id|.
   void OnStopCapture(int device_id);
 
   // IPC message: Pause capture on device referenced by |device_id|.
   void OnPauseCapture(int device_id);
 
   // IPC message: Receive an empty buffer from renderer. Send it to device
   // referenced by |device_id|.
   void OnReceiveEmptyBuffer(int device_id, int buffer_id);
@@ skipping 38 matching lines @@
   typedef std::map<VideoCaptureControllerID, Entry*> EntryMap;
   // A map of VideoCaptureControllerID to its state and VideoCaptureController.
   EntryMap entries_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoCaptureHost);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_HOST_H_