Implement accessibility support for CSS-transformed iframes.

content/browser/renderer_host/render_widget_host_view_base.cc

Index: content/browser/renderer_host/render_widget_host_view_base.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_base.cc b/content/browser/renderer_host/render_widget_host_view_base.cc
index d3dd8d044042810403ef4b6b09daf0ed6f1532c9..b411ca102f1a519c36e5f9c4353f5811bb1cdaca 100644
--- a/content/browser/renderer_host/render_widget_host_view_base.cc
+++ b/content/browser/renderer_host/render_widget_host_view_base.cc
@@ -392,6 +392,10 @@ void RenderWidgetHostViewBase::RemoveObserver(
   observers_.RemoveObserver(observer);
 }
 
+bool RenderWidgetHostViewBase::IsChildFrameForTesting() const {
+  return false;
+}
+
 cc::SurfaceId RenderWidgetHostViewBase::SurfaceIdForTesting() const {
   return cc::SurfaceId();
 }