FrameTree::Find only searches relative to local frames.

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

 /*
  * Copyright (C) 2010 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 4355 matching lines @@
   RegisterMockedHttpURLLoad("iframe_redirect.html");
   RegisterMockedHttpURLLoad("visible_iframe.html");
 
   FrameTestHelpers::WebViewHelper web_view_helper;
   web_view_helper.InitializeAndLoad(base_url_ + "iframe_redirect.html", true);
   // Pump pending requests one more time. The test page loads script that
   // navigates.
   FrameTestHelpers::PumpPendingRequestsForFrameToLoad(
       web_view_helper.WebView()->MainFrame());
 
-  WebFrame* iframe = web_view_helper.WebView()->FindFrameByName(
-      WebString::FromUTF8("ifr"), nullptr);
+  WebFrame* iframe = web_view_helper.WebView()
+                         ->MainFrame()
+                         ->ToWebLocalFrame()

[Łukasz Anforowicz, 2017/05/26 16:38:40]

ToWebLocalFrame above is okay, because otherwise the old code would have
returned null, trigerring ASSERT_TRUE(iframe) below.

[dcheng, 2017/05/26 18:28:06]

Ditto to using MainFrameImpl() here

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

Done (I think).

+                         ->FindFrameByName(WebString::FromUTF8("ifr"));
   ASSERT_TRUE(iframe);
   WebDataSource* iframe_data_source = iframe->DataSource();
   ASSERT_TRUE(iframe_data_source);
   WebVector<WebURL> redirects;
   iframe_data_source->RedirectChain(redirects);
   ASSERT_EQ(2U, redirects.size());
   EXPECT_EQ(ToKURL("about:blank"), KURL(redirects[0]));
   EXPECT_EQ(ToKURL("http://internal.test/visible_iframe.html"),
             KURL(redirects[1]));
 }
@@ skipping 7789 matching lines @@
     if (obj->IsText()) {
       LayoutText* layout_text = ToLayoutText(obj);
       text = layout_text->GetText();
       break;
     }
   }
   EXPECT_EQ("foo alt", text.Utf8());
 }
 
 }  // namespace blink