Crash in DirectX capturer

webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc

Index: webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc
diff --git a/webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc b/webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc
index b17c195340b0e495fa6e123a2b33c06141e9a2c5..2256e162fb4aa94be2052402f93744b8c396e6f0 100644
--- a/webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc
+++ b/webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc
@@ -285,9 +285,9 @@ void DxgiOutputDuplicator::Setup(Context* context) {
 }
 
 void DxgiOutputDuplicator::Unregister(const Context* const context) {
-  for (size_t i = 0; i < contexts_.size(); i++) {
-    if (contexts_[i] == context) {
-      contexts_[i] = nullptr;
+  for (auto it = contexts_.begin(); it != contexts_.end(); it++) {

[Sergey Ulanov, 2016/11/11 18:27:18]

This loop can be replaced with std::find:
  contexts_.erase(std::find(
      contexts_.begin(), contexts_.end(), context));

[Hzj_jie, 2016/11/11 21:51:31]

Done.

+    if (*it == context) {
+      contexts_.erase(it);

[Sergey Ulanov, 2016/11/11 18:27:18]

What was the reason this code was implemented this way? I.e. why was it
necessary to replace values with nullptr instead of erasing them?

[Hzj_jie, 2016/11/11 21:51:31]

Because std::vector::erase is O(n) instead of O(1). I over-optimized this logic.

[Sergey Ulanov, 2016/11/11 22:57:35]

FWIW it can be O(1) if you swap it with the last element, we don't care about
ordering here, but IMO it's better to keep this code simpler.

[Hzj_jie, 2016/11/11 23:28:22]

Oh, yes, since we have searched already. But the newer version should only
search once.

       return;
     }
   }
@@ -297,6 +297,7 @@ void DxgiOutputDuplicator::Unregister(const Context* const context) {
 
 void DxgiOutputDuplicator::SpreadContextChange(const Context* const source) {
   for (Context* dest : contexts_) {
+    RTC_DCHECK(dest);
     if (dest != source) {
       dest->updated_region.AddRegion(source->updated_region);
     }