This change fixes a crash issue in WindowCapturerWin. The issue and fix are both obvious, WindowCapturerWin should not return Result::SUCCESS with an empty frame. This issue was original introduced into the code base in change https://codereview.webrtc.org/1988783003/.

I am also considering whether we should move the
previous_size_ = frame->size();
window_size_map_[window_] = previous_size_;
into the true branch. But since this change needs to be merged into M58 and M59,
I would prefer to keep it as small as possible.

BUG=712615

Review-Url: https://codereview.webrtc.org/2835553002
Cr-Commit-Position: refs/heads/master@{#17799}
(cherry picked from commit d41af46)

Review-Url: https://codereview.webrtc.org/2834923002 .
Cr-Commit-Position: refs/branch-heads/59@{#2}
Cr-Branched-From: 10d095d-refs/heads/master@{#17657}

Author: Zijie He

webrtc/modules/desktop_capture/window_capturer_win.cc

@@ -252,12 +252,12 @@ void WindowCapturerWin::CaptureFrame() {
   frame->mutable_updated_region()->SetRect(
       DesktopRect::MakeSize(frame->size()));
 
-  if (!result) {
+  if (result) {
+    callback_->OnCaptureResult(Result::SUCCESS, std::move(frame));
+  } else {
     LOG(LS_ERROR) << "Both PrintWindow() and BitBlt() failed.";
-    frame.reset();
+    callback_->OnCaptureResult(Result::ERROR_TEMPORARY, nullptr);
   }
-
-  callback_->OnCaptureResult(Result::SUCCESS, std::move(frame));
 }
 
 }  // namespace