Use FrameTreeNode ID as frameId in extension APIs

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index a938e330d89984cf0a2911855a2209a2f6ea33ba..a56733dc4095303fc0f7d651652f991ddf7b14c7 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -764,6 +764,12 @@ RenderFrameHostImpl* WebContentsImpl::GetFocusedFrame() {
   return focused_node->current_frame_host();
 }
 
+RenderFrameHostImpl* WebContentsImpl::FindByFrameTreeNodeID(
+    int frame_tree_node_id) {
+  FrameTreeNode* frame = frame_tree_.FindByID(frame_tree_node_id);
+  return frame ? frame->current_frame_host() : nullptr;
+}
+
 void WebContentsImpl::ForEachFrame(
     const base::Callback<void(RenderFrameHost*)>& on_frame) {
   frame_tree_.ForEach(base::Bind(&ForEachFrameInternal, on_frame));