Update VectorDrawables cache at frame start

Draw VectorDrawables in GPU backed surface. Render VD cache
at the beginning of the frame to avoid context switching.

Test: CTS graphics tests pass.
Change-Id: Ia14e0ec4049c3fa87f03547fbda44043bf8dd793
diff --git a/libs/hwui/renderthread/CanvasContext.h b/libs/hwui/renderthread/CanvasContext.h
index 738c091..33eda96 100644
--- a/libs/hwui/renderthread/CanvasContext.h
+++ b/libs/hwui/renderthread/CanvasContext.h
@@ -194,6 +194,8 @@
 
     void waitOnFences();
 
+    IRenderPipeline* getRenderPipeline() { return mRenderPipeline.get(); }
+
 private:
     CanvasContext(RenderThread& thread, bool translucent, RenderNode* rootRenderNode,
             IContextFactory* contextFactory, std::unique_ptr<IRenderPipeline> renderPipeline);