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

content/browser/renderer_host/media/media_stream_provider.h

Index: content/browser/renderer_host/media/media_stream_provider.h
diff --git a/content/browser/renderer_host/media/media_stream_provider.h b/content/browser/renderer_host/media/media_stream_provider.h
index cab027a9bbca23552a9e6154487f439436a4006b..4f515cad26d78ada18b30098cf5dee6bcdaae40b 100644
--- a/content/browser/renderer_host/media/media_stream_provider.h
+++ b/content/browser/renderer_host/media/media_stream_provider.h
@@ -18,6 +18,10 @@
 #include "content/common/content_export.h"
 #include "content/common/media/media_stream_options.h"
 
+namespace base {
+class MessageLoopProxy;
+}
+
 namespace media_stream {
 
 enum MediaStreamProviderError {
@@ -59,8 +63,9 @@ class CONTENT_EXPORT 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* message_loop) = 0;
 
   // Unregisters the previously registered listener.
   virtual void Unregister() = 0;