Tab/Desktop Capture: Use requests instead of timer-based refreshing.

media/capture/content/thread_safe_capture_oracle.h

 // Copyright 2014 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.
 
 #ifndef MEDIA_CAPTURE_CONTENT_THREAD_SAFE_CAPTURE_ORACLE_H_
 #define MEDIA_CAPTURE_CONTENT_THREAD_SAFE_CAPTURE_ORACLE_H_
 
 #include <string>
 
 #include "base/memory/ref_counted.h"
@@ skipping 24 matching lines @@
                           bool enable_auto_throttling);
 
   // Called when a captured frame is available or an error has occurred.
   // If |success| is true then |frame| is valid and |timestamp| indicates when
   // the frame was painted.
   // If |success| is false, all other parameters are invalid.
   typedef base::Callback<void(const scoped_refptr<VideoFrame>& frame,
                               base::TimeTicks timestamp,
                               bool success)> CaptureFrameCallback;
 
+  // Record a change |event| along with its |damage_rect| and |event_time|, and
+  // then make a decision whether to proceed with capture. The decision is based
+  // on recent event history, capture activity, and the availability of
+  // resources.
+  //
+  // If this method returns false, the caller should take no further action.
+  // Otherwise, |storage| is set to the destination for the video frame capture;
+  // and, the caller should initiate capture, and then run |callback| once the
+  // video frame has been populated with its content.
   bool ObserveEventAndDecideCapture(VideoCaptureOracle::Event event,
                                     const gfx::Rect& damage_rect,
                                     base::TimeTicks event_time,
                                     scoped_refptr<VideoFrame>* storage,
                                     CaptureFrameCallback* callback);
 
+  // Attempt to re-send the last frame to the VideoCaptureDevice::Client.
+  // Returns true if successful. This can fail if the last frame is no longer
+  // available in the buffer pool, or if the VideoCaptureOracle decides to
+  // reject the "passive" refresh.
+  bool AttemptPassiveRefresh();
+
   base::TimeDelta min_capture_period() const {
     return oracle_.min_capture_period();
   }
 
   base::TimeTicks last_time_animation_was_detected() const {
     return oracle_.last_time_animation_was_detected();
   }
 
   gfx::Size max_frame_size() const {
     return params_.requested_format.frame_size;
@@ skipping 40 matching lines @@
   // Makes the decision to capture a frame.
   VideoCaptureOracle oracle_;
 
   // The video capture parameters used to construct the oracle proxy.
   const VideoCaptureParams params_;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_CAPTURE_CONTENT_THREAD_SAFE_CAPTURE_ORACLE_H_