Remove AboutToNavigateRenderFrame, issue custom notification for DevTools.

content/browser/frame_host/navigator_impl.cc

Index: content/browser/frame_host/navigator_impl.cc
diff --git a/content/browser/frame_host/navigator_impl.cc b/content/browser/frame_host/navigator_impl.cc
index f9028d9595438bd0e1340180d054bc7ffb31be5f..4ff9ffcc05ac4f8090817ce951d014ebc4e77e75 100644
--- a/content/browser/frame_host/navigator_impl.cc
+++ b/content/browser/frame_host/navigator_impl.cc
@@ -320,12 +320,6 @@ bool NavigatorImpl::NavigateToEntry(
   // Double check that here.
   CheckWebUIRendererDoesNotDisplayNormalURL(dest_render_frame_host, dest_url);
 
-  // Notify observers that we will navigate in this RenderFrame.
-  if (delegate_) {
-    delegate_->AboutToNavigateRenderFrame(frame_tree_node->current_frame_host(),
-                                          dest_render_frame_host);
-  }
-
   // Navigate in the desired RenderFrameHost.
   // We can skip this step in the rare case that this is a transfer navigation
   // which began in the chosen RenderFrameHost, since the request has already