Enable WebView overlays for Vulkan

This CL uses new skia api to determine if we're drawing on screen or
offscreen for vulkan and enables overlays when possible.

Bug: 185730234
Test: manual
Change-Id: Ib7748535431e4dc56b1af6d7ccc729b3b649df96
diff --git a/libs/hwui/WebViewFunctorManager.h b/libs/hwui/WebViewFunctorManager.h
index f28f310..0a02f2d 100644
--- a/libs/hwui/WebViewFunctorManager.h
+++ b/libs/hwui/WebViewFunctorManager.h
@@ -88,6 +88,7 @@
     }
 
 private:
+    bool prepareRootSurfaceControl();
     void reparentSurfaceControl(ASurfaceControl* parent);
 
 private: