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

media/capture/content/smooth_event_sampler.h

 // Copyright (c) 2015 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_SMOOTH_EVENT_SAMPLER_H_
 #define MEDIA_CAPTURE_SMOOTH_EVENT_SAMPLER_H_
 
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 // Filters a sequence of events to achieve a target frequency.
 class MEDIA_EXPORT SmoothEventSampler {
  public:
-  explicit SmoothEventSampler(base::TimeDelta min_capture_period);
+  enum {
+    // The maximum amount of time that can elapse before considering unchanged
+    // content as dirty for the purposes of timer-based overdue sampling.  This
+    // is the same value found in cc::FrameRateCounter.
+    OVERDUE_DIRTY_THRESHOLD_MILLIS = 250  // 4 FPS
+  };
+
+  SmoothEventSampler(base::TimeDelta min_capture_period,
+                     int redundant_capture_goal);
 
   // Get/Set minimum capture period. When setting a new value, the state of the
   // sampler is retained so that sampling will continue smoothly.
   base::TimeDelta min_capture_period() const { return min_capture_period_; }
   void SetMinCapturePeriod(base::TimeDelta p);
 
   // Add a new event to the event history, and consider whether it ought to be
   // sampled. The event is not recorded as a sample until RecordSample() is
   // called.
   void ConsiderPresentationEvent(base::TimeTicks event_time);
 
   // Returns true if the last event considered should be sampled.
   bool ShouldSample() const;
 
   // Operates on the last event added by ConsiderPresentationEvent(), marking
   // it as sampled. After this point we are current in the stream of events, as
   // we have sampled the most recent event.
   void RecordSample();
 
+  // Returns true if, at time |event_time|, sampling should occur because too
+  // much time will have passed relative to the last event and/or sample.
+  bool IsOverdueForSamplingAt(base::TimeTicks event_time) const;
+
   // Returns true if ConsiderPresentationEvent() has been called since the last
   // call to RecordSample().
   bool HasUnrecordedEvent() const;
 
  private:
   base::TimeDelta min_capture_period_;
+  const int redundant_capture_goal_;
   base::TimeDelta token_bucket_capacity_;
 
   base::TimeTicks current_event_;
   base::TimeTicks last_sample_;
+  int overdue_sample_count_;
   base::TimeDelta token_bucket_;
 
   DISALLOW_COPY_AND_ASSIGN(SmoothEventSampler);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_CAPTURE_SMOOTH_EVENT_SAMPLER_H_