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

content/public/test/browser_test_utils.cc

Index: content/public/test/browser_test_utils.cc
diff --git a/content/public/test/browser_test_utils.cc b/content/public/test/browser_test_utils.cc
index 0864b5a2ae4d89bf797a839f21ec40f8e937e24a..f8ebb882ae270176a5266368db6087904d41b6e7 100644
--- a/content/public/test/browser_test_utils.cc
+++ b/content/public/test/browser_test_utils.cc
@@ -935,8 +935,8 @@ RenderFrameHost* FrameMatchingPredicate(
   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) {