Enable WebViewAccessiblityTest for OOPIF webview.

content/browser/frame_host/render_frame_host_delegate.cc

Index: content/browser/frame_host/render_frame_host_delegate.cc
diff --git a/content/browser/frame_host/render_frame_host_delegate.cc b/content/browser/frame_host/render_frame_host_delegate.cc
index 7314dcbc4114839d89ae9520f8e17e1611bf3298..39220a958ea70d9ac0977d8fb92997d3adac2daa 100644
--- a/content/browser/frame_host/render_frame_host_delegate.cc
+++ b/content/browser/frame_host/render_frame_host_delegate.cc
@@ -93,6 +93,11 @@ bool RenderFrameHostDelegate::ShouldRouteMessageEvent(
   return false;
 }
 
+RenderFrameHost* RenderFrameHostDelegate::GetFrameAtNode(
+    FrameTreeNode* tree_node) {
+  return nullptr;
+}
+
 std::unique_ptr<WebUIImpl>
 RenderFrameHostDelegate::CreateWebUIForRenderFrameHost(const GURL& url) {
   return nullptr;