FrameTree::Find only searches relative to local frames.

third_party/WebKit/Source/web/tests/LayoutGeometryMapTest.cpp

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 48 matching lines @@
   void TearDown() override {
     Platform::Current()
         ->GetURLLoaderMockFactory()
         ->UnregisterAllURLsAndClearMemoryCache();
   }
 
  protected:
   static LayoutBox* GetFrameElement(const char* iframe_name,
                                     WebView* web_view,
                                     const WTF::AtomicString& element_id) {
-    WebLocalFrameImpl* iframe = ToWebLocalFrameImpl(
-        web_view->FindFrameByName(WebString::FromUTF8(iframe_name)));
-    if (!iframe)
+    if (!web_view->MainFrame()->IsWebLocalFrame())

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

As this is a unit test, you can cheat and just use MainFrameImpl() without
checking.

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

Done (I think, I hope I've correctly understood what you meant here).

[dcheng, 2017/05/26 20:16:19]

Ah.... the problem is this test isn't plumbing things through with the right
types: it should be plumbing them through as WebViewImpl (since that's what it
starts with). I guess fixing this completely correctly is out of scope since it
touches a lot of things. Good enough for now.

       return nullptr;
-    LocalFrame* frame = iframe->GetFrame();
+    WebFrame* iframe =
+        web_view->MainFrame()->ToWebLocalFrame()->FindFrameByName(
+            WebString::FromUTF8(iframe_name));
+    if (!iframe || !iframe->IsWebLocalFrame())
+      return nullptr;
+    LocalFrame* frame = ToWebLocalFrameImpl(iframe)->GetFrame();
     Document* doc = frame->GetDocument();
     Element* element = doc->getElementById(element_id);
     if (!element)
       return nullptr;
     return element->GetLayoutBox();
   }
 
   static Element* GetElement(WebView* web_view,
                              const WTF::AtomicString& element_id) {
     WebViewBase* web_view_impl = static_cast<WebViewBase*>(web_view);
@@ skipping 445 matching lines @@
   EXPECT_EQ(FloatRect(263.0f, 154.0f, 10.0f, 8.0f),
             RectFromQuad(rgm.MapToAncestor(rect, nullptr)));
 
   rgm.PushMappingsToAncestor(floating, span);
   EXPECT_EQ(rect, RectFromQuad(rgm.MapToAncestor(rect, container)));
   EXPECT_EQ(FloatRect(63.0f, 54.0f, 10.0f, 8.0f),
             RectFromQuad(rgm.MapToAncestor(rect, nullptr)));
 }
 
 }  // namespace blink