Several minor improvements of DirectX capturer

webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 129 matching lines @@
     return false;
   }
 
   // We need to merge updated region with the one from last frame, since current
   // frame contains the content one frame before. Note, this is for double
   // buffering implementation, as what we have in ScreenCapturerWinDirectx. If
   // a consumer uses single buffering, we should clear context->updated_region
   // after it has been merged to updated_region.
   DesktopRegion updated_region;
   updated_region.Swap(&context->updated_region);
-  if (error.Error() == S_OK && frame_info.AccumulatedFrames > 0) {
+  if (error.Error() == S_OK &&
+      frame_info.AccumulatedFrames > 0 &&
+      resource) {

[Jamie, 2016/09/17 00:49:30]

Please add something to the CL description for this change.

[Hzj_jie, 2016/09/19 19:09:57]

Done.

     DetectUpdatedRegion(frame_info, offset, &context->updated_region);
     if (!texture_->CopyFrom(frame_info, resource.Get(),
                             context->updated_region)) {
       return false;
     }
     SpreadContextChange(context);
     updated_region.AddRegion(context->updated_region);
 
     const DesktopFrame& source = texture_->AsDesktopFrame();
     for (DesktopRegion::Iterator it(updated_region); !it.IsAtEnd();
@@ skipping 147 matching lines @@
 }
 
 DesktopRect DxgiOutputDuplicator::TargetRect(DesktopRect rect,
                                              DesktopVector offset) {
   rect = SourceRect(rect);
   rect.Translate(offset);
   return rect;
 }
 
 }  // namespace webrtc