[DesktopCapturer] FallbackDesktopCapturerWrapper and its tests

webrtc/modules/desktop_capture/fake_desktop_capturer.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.
  */
 
 #include "webrtc/modules/desktop_capture/fake_desktop_capturer.h"
 
 #include <utility>
 
 namespace webrtc {
 
-FakeDesktopCapturer::FakeDesktopCapturer()
-    : callback_(nullptr),
-      result_(DesktopCapturer::Result::SUCCESS),
-      generator_(nullptr) {}
-
+FakeDesktopCapturer::FakeDesktopCapturer() = default;
 FakeDesktopCapturer::~FakeDesktopCapturer() = default;
 
 void FakeDesktopCapturer::set_result(DesktopCapturer::Result result) {
   result_ = result;
 }
 
+int FakeDesktopCapturer::num_frames_captured() const {
+  return num_frames_captured_;
+}
+
+int FakeDesktopCapturer::num_capture_attempts() const {
+  return num_capture_attempts_;
+}
+
 // Uses the |generator| provided as DesktopFrameGenerator, FakeDesktopCapturer
 // does
 // not take the ownership of |generator|.
 void FakeDesktopCapturer::set_frame_generator(
     DesktopFrameGenerator* generator) {
   generator_ = generator;
 }
 
 void FakeDesktopCapturer::Start(DesktopCapturer::Callback* callback) {
   callback_ = callback;
 }
 
 void FakeDesktopCapturer::CaptureFrame() {
+  num_capture_attempts_++;
   if (generator_) {
+    if (result_ != DesktopCapturer::Result::SUCCESS) {
+      callback_->OnCaptureResult(result_, nullptr);
+      return;
+    }
+
     std::unique_ptr<DesktopFrame> frame(
         generator_->GetNextFrame(shared_memory_factory_.get()));
     if (frame) {
+      num_frames_captured_++;
       callback_->OnCaptureResult(result_, std::move(frame));
     } else {
       callback_->OnCaptureResult(DesktopCapturer::Result::ERROR_TEMPORARY,
                                  nullptr);
     }
     return;
   }
   callback_->OnCaptureResult(DesktopCapturer::Result::ERROR_PERMANENT, nullptr);
 }
 
 void FakeDesktopCapturer::SetSharedMemoryFactory(
     std::unique_ptr<SharedMemoryFactory> shared_memory_factory) {
   shared_memory_factory_ = std::move(shared_memory_factory);
 }
 
 bool FakeDesktopCapturer::GetSourceList(DesktopCapturer::SourceList* sources) {
   sources->push_back({kWindowId, "A-Fake-DesktopCapturer-Window"});
   sources->push_back({kScreenId});
   return true;
 }
 
 bool FakeDesktopCapturer::SelectSource(DesktopCapturer::SourceId id) {
   return id == kWindowId || id == kScreenId || id == kFullDesktopScreenId;
 }
 
 }  // namespace webrtc