Screen Video Capture: Implement suspend optimization.

media/capture/content/screen_capture_device_core.h

Index: media/capture/content/screen_capture_device_core.h
diff --git a/media/capture/content/screen_capture_device_core.h b/media/capture/content/screen_capture_device_core.h
index 3f8884b3c857c8fd9f87fbe21d94a0eb7f1b7ffa..c965043e4820f3f9d79cbe66448b3e6aeef2b209 100644
--- a/media/capture/content/screen_capture_device_core.h
+++ b/media/capture/content/screen_capture_device_core.h
@@ -37,6 +37,10 @@ class CAPTURE_EXPORT VideoCaptureMachine {
                      const VideoCaptureParams& params,
                      const base::Callback<void(bool)> callback) = 0;
 
+  // Suspend/Resume frame delivery. Implementations of these are optional.
+  virtual void Suspend() {}
+  virtual void Resume() {}
+
   // Stops capturing.
   // |callback| is invoked after the capturing has stopped.
   virtual void Stop(const base::Closure& callback) = 0;
@@ -82,11 +86,13 @@ class CAPTURE_EXPORT ScreenCaptureDeviceCore
   void AllocateAndStart(const VideoCaptureParams& params,
                         std::unique_ptr<VideoCaptureDevice::Client> client);
   void RequestRefreshFrame();
+  void Suspend();
+  void Resume();
   void StopAndDeAllocate();
 
  private:
   // Flag indicating current state.
-  enum State { kIdle, kCapturing, kError, kLastCaptureState };
+  enum State { kIdle, kCapturing, kSuspended, kError, kLastCaptureState };
 
   void TransitionStateTo(State next_state);