Create video and audio decoder threads on demand.

media/base/message_loop_factory.h

Index: media/base/message_loop_factory.h
diff --git a/media/base/message_loop_factory.h b/media/base/message_loop_factory.h
index d8ecdb56cb823c6d991273aac53b0f7686ecaaa2..b67165c365001ef677ceb25fb384ab77aa729bea 100644
--- a/media/base/message_loop_factory.h
+++ b/media/base/message_loop_factory.h
@@ -33,7 +33,7 @@ class MEDIA_EXPORT MessageLoopFactory {
   // is created if the factory doesn't have one associated with |name|.
   //
   // |name| must not be an empty string.
-  MessageLoop* GetMessageLoop(const std::string& name);
+  virtual MessageLoop* GetMessageLoop(const std::string& name);
 
   // Get the message loop proxy associated with |name|. A new MessageLoopProxy
   // is created if the factory doesn't have one associated with |name|.
@@ -42,11 +42,12 @@ class MEDIA_EXPORT MessageLoopFactory {
   scoped_refptr<base::MessageLoopProxy> GetMessageLoopProxy(
       const std::string& name);
 
- private:
+ protected:
   // Only allow scoped_ptr<> to delete factory.
   friend class scoped_ptr<MessageLoopFactory>;
-  ~MessageLoopFactory();
+  virtual ~MessageLoopFactory();
 
+ private:
   // Returns the thread associated with |name| creating a new thread if needed.
   base::Thread* GetThread(const std::string& name);