FrameTree::Find only searches relative to local frames.

content/shell/test_runner/test_runner_for_specific_view.cc

Index: content/shell/test_runner/test_runner_for_specific_view.cc
diff --git a/content/shell/test_runner/test_runner_for_specific_view.cc b/content/shell/test_runner/test_runner_for_specific_view.cc
index cbd139b1d53620b70e371556029b54040d073fac..aaac02280c405d337c2663444f8a19b8f81c04a3 100644
--- a/content/shell/test_runner/test_runner_for_specific_view.cc
+++ b/content/shell/test_runner/test_runner_for_specific_view.cc
@@ -679,8 +679,12 @@ std::string TestRunnerForSpecificView::SelectionAsMarkup() {
 
 void TestRunnerForSpecificView::SetViewSourceForFrame(const std::string& name,
                                                       bool enabled) {
+  if (!web_view()->MainFrame()->IsWebLocalFrame())

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

Is this something we'll need to fix at some point? I guess it's probably not a
new problem though...

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

Possibly.  For now, let me just do what other similar methods in this source
file do: CHECK(...) that main frame is local.  If any test starts to need OOPIF
support here then the CHECK(...) will hopefully quickly guide them to the
realization that OOPIF support is missing.

+    return;
+
   WebFrame* target_frame =
-      web_view()->FindFrameByName(WebString::FromUTF8(name));
+      web_view()->MainFrame()->ToWebLocalFrame()->FindFrameByName(
+          WebString::FromUTF8(name));
   if (target_frame)
     target_frame->EnableViewSourceMode(enabled);
 }