FrameTree::Find only searches relative to local frames.

third_party/WebKit/Source/web/WebLocalFrameImpl.cpp

Index: third_party/WebKit/Source/web/WebLocalFrameImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebLocalFrameImpl.cpp b/third_party/WebKit/Source/web/WebLocalFrameImpl.cpp
index 25513bd30a24152b3a9ae62443c657a1b4278e4c..c5626ba0a5bd1df898431072e09daec99f058ec3 100644
--- a/third_party/WebKit/Source/web/WebLocalFrameImpl.cpp
+++ b/third_party/WebKit/Source/web/WebLocalFrameImpl.cpp
@@ -2016,6 +2016,11 @@ WebLocalFrameImpl* WebLocalFrameImpl::LocalRoot() {
   return local_root;
 }
 
+WebFrame* WebLocalFrameImpl::FindFrameByName(const WebString& name) {
+  Frame* result = GetFrame()->Tree().Find(name);
+  return WebFrame::FromFrame(result);

[dcheng, 2017/05/26 18:28:05]

The original helper on WebView only returned local frames it looks like (and
returned nullptr otherwise). Do you think we should keep the same interface?

[Łukasz Anforowicz, 2017/05/26 20:04:05]

I think these 2 concerns (finding a frame by name in the browsing instance VS
figuring out if a frame is local) are separate and should not be shoehorned into
FindFrameByName (FindFrameByNameAndCheckIfResultIsALocalFrame?).  The callers
who need to check if the frame is local (only some of the tests AFAICT) can
always call result->IsWebLocalFrame() after calling FindFrameByName.

+}
+
 void WebLocalFrameImpl::SendPings(const WebURL& destination_url) {
   DCHECK(GetFrame());
   DCHECK(context_menu_node_.Get());