Unified BeginFrame scheduling

ui/base/android/window_android.cc

Index: ui/base/android/window_android.cc
diff --git a/ui/base/android/window_android.cc b/ui/base/android/window_android.cc
index 490c6f3b545f2adfaabf67d3e4efb2766fed84f9..4041a3d9ba9c96e28e6b5a4e58bc3319c2f09e89 100644
--- a/ui/base/android/window_android.cc
+++ b/ui/base/android/window_android.cc
@@ -65,10 +65,11 @@ void WindowAndroid::AttachCompositor(WindowAndroidCompositor* compositor) {
 }
 
 void WindowAndroid::DetachCompositor() {
-  compositor_ = NULL;
   FOR_EACH_OBSERVER(WindowAndroidObserver,
                     observer_list_,
                     OnDetachCompositor());
+  // Makes |compositor_| NULL after all observers finishes their work.
+  compositor_ = NULL;
   observer_list_.Clear();
 }