Ensure Dxgi duplicator works correctly in session 0

webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h

 /*
  *  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 42 matching lines @@
     // D3D_FEATURE_LEVEL has been retrieved from underlying OS APIs.
     D3D_FEATURE_LEVEL min_feature_level;
     D3D_FEATURE_LEVEL max_feature_level;
 
     // TODO(zijiehe): Add more fields, such as manufacturer name, mode, driver
     // version.
   };
 
   enum class Result {
     SUCCEEDED,
+    UNSUPPORTED_SESSION,
     FRAME_PREPARE_FAILED,
     INITIALIZATION_FAILED,
     DUPLICATION_FAILED,
     INVALID_MONITOR_ID,
   };
 
   // Returns the singleton instance of DxgiDuplicatorController.
   static rtc::scoped_refptr<DxgiDuplicatorController> Instance();
 
   // All the following public functions implicitly call Initialize() function.
 
   // Detects whether the system supports DXGI based capturer.
   bool IsSupported();
 
-  // Returns a copy of D3dInfo composed by last Initialize() function call.
+  // Returns a copy of D3dInfo composed by last Initialize() function call. This
+  // function always copies the latest information into |info|. But once the
+  // function returns false, the information in |info| may not accurate.
   bool RetrieveD3dInfo(D3dInfo* info);
 
   // Captures current screen and writes into |frame|.
   // TODO(zijiehe): Windows cannot guarantee the frames returned by each
   // IDXGIOutputDuplication are synchronized. But we are using a totally
   // different threading model than the way Windows suggested, it's hard to
   // synchronize them manually. We should find a way to do it.
   Result Duplicate(DxgiFrame* frame);
 
   // Captures one monitor and writes into target. |monitor_id| should >= 0. If
@@ skipping 116 matching lines @@
   rtc::CriticalSection lock_;
 
   // A self-incremented integer to compare with the one in Context. It ensures
   // a Context instance is always initialized after DxgiDuplicatorController.
   int identity_ = 0;
   DesktopRect desktop_rect_;
   DesktopVector dpi_;
   std::vector<DxgiAdapterDuplicator> duplicators_;
   D3dInfo d3d_info_;
   ResolutionChangeDetector resolution_change_detector_;
+  // A number to indicate how many succeeded duplications have been performed.
+  uint32_t succeeded_duplications_ = 0;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_WIN_DXGI_DUPLICATOR_CONTROLLER_H_