Move the device enumerate/open/close work to device thread from IO thread

content/browser/renderer_host/media/media_stream_provider.h

 // Copyright (c) 2011 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.
 
 // MediaStreamProvider is used to capture media of the types defined in
 // MediaStreamType. There is only one MediaStreamProvider instance per media
 // type and a MediaStreamProvider instance can have only one registered
 // listener.
 // The MediaStreamManager is expected to be called on Browser::IO thread and
 // the listener will be called on the same thread.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_MEDIA_STREAM_PROVIDER_H_
 #define CONTENT_BROWSER_RENDERER_HOST_MEDIA_MEDIA_STREAM_PROVIDER_H_
 
 #include <list>
 #include <string>
 
 #include "content/common/content_export.h"
 #include "content/common/media/media_stream_options.h"
 
+namespace base {
+class MessageLoopProxy;
+}
+
 namespace media_stream {
 
 enum MediaStreamProviderError {
   kMediaStreamOk = 0,
   kInvalidMediaStreamType,
   kInvalidSession,
   kUnknownSession,
   kDeviceNotAvailable,
   kDeviceAlreadyInUse,
   kUnknownError
@@ skipping 21 matching lines @@
                      int capture_session_id,
                      MediaStreamProviderError error) = 0;
 
  protected:
   virtual ~MediaStreamProviderListener() {}
 };
 
 // Implemented by a manager class providing captured media.
 class CONTENT_EXPORT MediaStreamProvider {
  public:
-  // Registers a listener, only one listener is allowed.
-  virtual void Register(MediaStreamProviderListener* listener) = 0;
+  // Registers a listener and a device message loop.
+  virtual void Register(MediaStreamProviderListener* listener,
+                        base::MessageLoopProxy* device_thread_loop) = 0;
 
   // Unregisters the previously registered listener.
   virtual void Unregister() = 0;
 
   // Enumerates existing capture devices and calls |DevicesEnumerated|.
   virtual void EnumerateDevices() = 0;
 
   // Opens the specified device. The device is not started and it is still
   // possible for other applications to open the device before the device is
   // started. |Opened| is called when the device is opened.
   // kInvalidMediaCaptureSessionId is returned on error.
   virtual int Open(const StreamDeviceInfo& device) = 0;
 
   // Closes the specified device and calls |Closed| when done.
   virtual void Close(int capture_session_id) = 0;
 
  protected:
   virtual ~MediaStreamProvider() {}
 };
 
 }  // namespace media_stream
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_MEDIA_STREAM_PROVIDER_H_