ui freeze workaround: reenable triple buffering mode

we're seeing UI freezes when window updates and
composition are separated. for now we workaround this
by always doing a composition after window updates on
vsync. triple buffering is reenabled for performance.

Change-Id: I693d705000b7452489bb0b4918fbeadb9879315c
diff --git a/services/surfaceflinger/MessageQueue.cpp b/services/surfaceflinger/MessageQueue.cpp
index 1ff3567..290fff4 100644
--- a/services/surfaceflinger/MessageQueue.cpp
+++ b/services/surfaceflinger/MessageQueue.cpp
@@ -133,7 +133,8 @@
 }
 
 void MessageQueue::invalidate() {
-    mHandler->signalInvalidate();
+//    mHandler->signalInvalidate();
+    mEvents->requestNextVsync();
 }
 
 void MessageQueue::refresh() {