Fix segfault when unplugging captured external display

content/browser/media/capture/desktop_capture_device_aura.cc

Index: content/browser/media/capture/desktop_capture_device_aura.cc
diff --git a/content/browser/media/capture/desktop_capture_device_aura.cc b/content/browser/media/capture/desktop_capture_device_aura.cc
index 6b6557f1844058b74dc539b5d6b24289630dbaba..81ee8e2647ec6adf9bf573ff9637124c9b2b6934 100644
--- a/content/browser/media/capture/desktop_capture_device_aura.cc
+++ b/content/browser/media/capture/desktop_capture_device_aura.cc
@@ -235,7 +235,8 @@ void DesktopVideoCaptureMachine::Stop(const base::Closure& callback) {
 
   // Stop observing compositor and window events.
   if (desktop_window_) {
-    if (desktop_window_->GetHost())
+    // In the host destructor the compositor is destroyed before the window

[Sergey Ulanov, 2014/12/12 17:42:34]

nit: add . at the end of the comment

+    if (desktop_window_->GetHost() && desktop_window_->GetHost()->compositor())

[Sergey Ulanov, 2014/12/12 17:42:34]

Store GetHost() result so it doesn't have to be called 3 times, i.e.:
 WindowTreeHost* window_host = desktop_window_->GetHost();
 if (window_host && window_host->compositor())
   window_host->compositor()->RemoveObserver(this);

       desktop_window_->GetHost()->compositor()->RemoveObserver(this);
     desktop_window_->RemoveObserver(this);
     desktop_window_ = NULL;