Update VideoFramePump to pass un-changed frames to encoders.

remoting/codec/video_encoder_verbatim.cc

 // Copyright (c) 2012 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.
 
 #include "remoting/codec/video_encoder_verbatim.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "base/time/time.h"
 #include "remoting/base/util.h"
 #include "remoting/proto/video.pb.h"
 #include "third_party/webrtc/modules/desktop_capture/desktop_frame.h"
 #include "third_party/webrtc/modules/desktop_capture/desktop_geometry.h"
 #include "third_party/webrtc/modules/desktop_capture/desktop_region.h"
 
 namespace remoting {
 
 static uint8_t* GetPacketOutputBuffer(VideoPacket* packet, size_t size) {
   packet->mutable_data()->resize(size);
   return reinterpret_cast<uint8_t*>(string_as_array(packet->mutable_data()));
 }
 
 VideoEncoderVerbatim::VideoEncoderVerbatim() {}
 VideoEncoderVerbatim::~VideoEncoderVerbatim() {}
 
 scoped_ptr<VideoPacket> VideoEncoderVerbatim::Encode(
     const webrtc::DesktopFrame& frame) {
-  CHECK(frame.data());
+  DCHECK(frame.data());
+
+  // If nothing has changed in the frame then return NULL to indicate that
+  // we don't need to actually send anything (e.g. nothing to top-off).
+  if (frame.updated_region().is_empty())
+    return nullptr;
 
   base::Time encode_start_time = base::Time::Now();
 
   // Create a VideoPacket with common fields (e.g. DPI, rects, shape) set.
   scoped_ptr<VideoPacket> packet(helper_.CreateVideoPacket(frame));
   packet->mutable_format()->set_encoding(VideoPacketFormat::ENCODING_VERBATIM);
 
   // Calculate output size.
   size_t output_size = 0;
   for (webrtc::DesktopRegion::Iterator iter(frame.updated_region());
@@ skipping 21 matching lines @@
   }
 
   // Note the time taken to encode the pixel data.
   packet->set_encode_time_ms(
       (base::Time::Now() - encode_start_time).InMillisecondsRoundedUp());
 
   return packet.Pass();
 }
 
 }  // namespace remoting