Resume RT-animations after a pauseSurface

Bug: 18203577

The issue occurs as a result of performTraversals() both doing
a window relayout call *and* early-returning because it's not dirty.

To fix this pauseSurface() returns whether or not the RT-side is
"dirty" to force ViewRootImpl to do a draw even if mDirty is
otherwise empty.

Change-Id: I534f367e75d18d273ebf14df3927f5c464ef6bef
diff --git a/libs/hwui/renderthread/CanvasContext.h b/libs/hwui/renderthread/CanvasContext.h
index 435244e..0cc2c7c 100644
--- a/libs/hwui/renderthread/CanvasContext.h
+++ b/libs/hwui/renderthread/CanvasContext.h
@@ -67,7 +67,7 @@
 
     bool initialize(ANativeWindow* window);
     void updateSurface(ANativeWindow* window);
-    void pauseSurface(ANativeWindow* window);
+    bool pauseSurface(ANativeWindow* window);
     bool hasSurface() { return mNativeWindow.get(); }
 
     void setup(int width, int height, const Vector3& lightCenter, float lightRadius,