Store GrContext on RenderThread for use by Skia-based renderers.

Test: built and booted on device
Change-Id: I4c1060ec72bc67e54e6b2d25b1f2c13aaa513f89
diff --git a/libs/hwui/renderthread/CanvasContext.h b/libs/hwui/renderthread/CanvasContext.h
index 559ac87..125f109 100644
--- a/libs/hwui/renderthread/CanvasContext.h
+++ b/libs/hwui/renderthread/CanvasContext.h
@@ -89,7 +89,7 @@
      * If Properties::isSkiaEnabled() is true then this will return the Skia
      * grContext associated with the current RenderPipeline.
      */
-    GrContext* getGrContext() const { return mRenderPipeline->getGrContext(); }
+    GrContext* getGrContext() const { return mRenderThread.getGrContext(); }
 
     // Won't take effect until next EGLSurface creation
     void setSwapBehavior(SwapBehavior swapBehavior);