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 8a4e0ed3bc16025a8c8c722ff7180b08ac7fd2ae..d26263942be7fb2d8756353268fc46f4e2ee893a 100644
--- a/content/browser/renderer_host/render_widget_host_view_base.cc
+++ b/content/browser/renderer_host/render_widget_host_view_base.cc
@@ -730,6 +730,10 @@ void RenderWidgetHostViewBase::RemoveObserver(
   observers_.RemoveObserver(observer);
 }
 
+bool RenderWidgetHostViewBase::IsChildFrameForTesting() const {
+  return false;
+}
+
 cc::SurfaceId RenderWidgetHostViewBase::SurfaceIdForTesting() const {
   return cc::SurfaceId();
 }