Fix some edge cases

Bug: 27709981

This desperately needs a refactor, but to keep
the current (really needed & nice) behavior of
dispatching after sync finishes would be difficult
to handle cleanly without lots of ripping so... #yolo

Change-Id: I831a06c6ae7412a062720d68ecbe3085190f0258
diff --git a/libs/hwui/renderthread/DrawFrameTask.h b/libs/hwui/renderthread/DrawFrameTask.h
index cae251a9..9bba065 100644
--- a/libs/hwui/renderthread/DrawFrameTask.h
+++ b/libs/hwui/renderthread/DrawFrameTask.h
@@ -62,7 +62,7 @@
     void pushLayerUpdate(DeferredLayerUpdater* layer);
     void removeLayerUpdate(DeferredLayerUpdater* layer);
 
-    int drawFrame();
+    int drawFrame(TreeObserver* observer);
 
     int64_t* frameInfo() { return mFrameInfo; }
 
@@ -87,6 +87,7 @@
 
     int mSyncResult;
     int64_t mSyncQueued;
+    TreeObserver* mObserver;
 
     int64_t mFrameInfo[UI_THREAD_FRAME_INFO_SIZE];
 };