Add support for drawLayer CanvasOps

Introdcued DrawLayer CanvasOp and implementation
Test in progress with support for GrRecrodingContext backed
SkDevices.

Test: In progress
Change-Id: I53c58233536a78c20b867d659eae2dae2adc54b2
diff --git a/libs/hwui/Layer.h b/libs/hwui/Layer.h
index ea3bfc9..e99e762 100644
--- a/libs/hwui/Layer.h
+++ b/libs/hwui/Layer.h
@@ -21,6 +21,7 @@
 #include <SkBlendMode.h>
 #include <SkColorFilter.h>
 #include <SkColorSpace.h>
+#include <SkCanvas.h>
 #include <SkPaint.h>
 #include <SkImage.h>
 #include <SkMatrix.h>
@@ -87,6 +88,8 @@
 
     inline sk_sp<SkImage> getImage() const { return this->layerImage; }
 
+    void draw(SkCanvas* canvas);
+
 protected:
 
     RenderState& mRenderState;