Do not reinvent the wheel / use content APIs to find a frame by name.

content/public/test/browser_test_utils.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/public/test/browser_test_utils.h"
 
 #include <stddef.h>
 #include <tuple>
 #include <utility>
 
@@ skipping 917 matching lines @@
     frame_set->insert(host);
 }
 }
 
 RenderFrameHost* FrameMatchingPredicate(
     WebContents* web_contents,
     const base::Callback<bool(RenderFrameHost*)>& predicate) {
   std::set<RenderFrameHost*> frame_set;
   web_contents->ForEachFrame(
       base::Bind(&AddToSetIfFrameMatchesPredicate, &frame_set, predicate));
-  DCHECK_EQ(1U, frame_set.size());
-  return *frame_set.begin();
+  EXPECT_EQ(1U, frame_set.size());
+  return frame_set.size() == 1 ? *frame_set.begin() : nullptr;
 }
 
 bool FrameMatchesName(const std::string& name, RenderFrameHost* frame) {
   return frame->GetFrameName() == name;
 }
 
 bool FrameIsChildOfMainFrame(RenderFrameHost* frame) {
   return frame->GetParent() && !frame->GetParent()->GetParent();
 }
 
@@ skipping 1081 matching lines @@
                                  bool user_gesture,
                                  bool last_unlocked_by_target,
                                  bool privileged) {
   IPC::IpcSecurityTestUtil::PwnMessageReceived(
       process->GetChannel(),
       ViewHostMsg_LockMouse(routing_id, user_gesture, last_unlocked_by_target,
                             privileged));
 }
 
 }  // namespace content