Fix bug in keeping capture in sync during destruction

ui/aura/mus/capture_synchronizer.cc

Index: ui/aura/mus/capture_synchronizer.cc
diff --git a/ui/aura/mus/capture_synchronizer.cc b/ui/aura/mus/capture_synchronizer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..74f2500aad9cbb517541099e414cf49689053dbd
--- /dev/null
+++ b/ui/aura/mus/capture_synchronizer.cc
@@ -0,0 +1,81 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/aura/mus/capture_synchronizer.h"
+
+#include "base/auto_reset.h"
+#include "services/ui/public/interfaces/window_tree.mojom.h"
+#include "ui/aura/client/capture_client.h"
+#include "ui/aura/mus/capture_synchronizer_delegate.h"
+#include "ui/aura/mus/window_mus.h"
+#include "ui/aura/window.h"
+
+namespace aura {
+
+CaptureSynchronizer::CaptureSynchronizer(CaptureSynchronizerDelegate* delegate,
+                                         ui::mojom::WindowTree* window_tree,
+                                         client::CaptureClient* capture_client)
+    : delegate_(delegate),
+      window_tree_(window_tree),
+      capture_client_(capture_client) {
+  capture_client_->AddObserver(this);
+}
+
+CaptureSynchronizer::~CaptureSynchronizer() {
+  SetCaptureWindow(nullptr);
+  capture_client_->RemoveObserver(this);
+}
+
+void CaptureSynchronizer::SetCaptureFromServer(WindowMus* window) {
+  if (window == capture_window_)
+    return;
+
+  DCHECK(!setting_capture_);
+  // Don't immediatley set |capture_client_|. It's possible the change will be

[msw, 2016/10/31 17:56:20]

nit: immediately.

[sky, 2016/10/31 18:00:31]

Done.

+  // rejected.
+  base::AutoReset<bool> capture_reset(&setting_capture_, true);
+  base::AutoReset<WindowMus*> window_setting_capture_to_reset(
+      &window_setting_capture_to_, window);
+  capture_client_->SetCapture(window ? window->GetWindow() : nullptr);
+}
+
+void CaptureSynchronizer::SetCaptureWindow(WindowMus* window) {
+  if (capture_window_)
+    capture_window_->GetWindow()->RemoveObserver(this);
+  capture_window_ = window;
+  if (capture_window_)
+    capture_window_->GetWindow()->AddObserver(this);
+}
+
+void CaptureSynchronizer::OnWindowDestroying(Window* window) {
+  // The CaptureClient implementation handles resetting capture when a window
+  // is destroyed, but because of observer ordering this may be called first.
+  DCHECK_EQ(window, capture_window_->GetWindow());
+  SetCaptureWindow(nullptr);
+  // The server will release capture when a window is destroyed, so no need
+  // explicitly schedule a change.
+}
+
+void CaptureSynchronizer::OnCaptureChanged(Window* lost_capture,
+                                           Window* gained_capture) {
+  if (!gained_capture && !capture_window_)
+    return;  // Happens if window deleted during notification.

[msw, 2016/10/31 17:56:20]

nit: 'the window is deleted'

[sky, 2016/10/31 18:00:31]

Done.

+
+  WindowMus* gained_capture_mus = WindowMus::Get(gained_capture);
+  if (setting_capture_ && gained_capture_mus == window_setting_capture_to_) {
+    SetCaptureWindow(gained_capture_mus);
+    return;
+  }
+
+  const uint32_t change_id =
+      delegate_->CreateChangeIdForCapture(capture_window_);
+  WindowMus* old_capture_window = capture_window_;
+  SetCaptureWindow(gained_capture_mus);
+  if (capture_window_)
+    window_tree_->SetCapture(change_id, capture_window_->server_id());
+  else
+    window_tree_->ReleaseCapture(change_id, old_capture_window->server_id());
+}
+
+}  // namespace aura