Extend the ToRenderFrameHost magic to FrameTreeNode* and Shell*

content/test/webrtc_content_browsertest_base.cc

Index: content/test/webrtc_content_browsertest_base.cc
diff --git a/content/test/webrtc_content_browsertest_base.cc b/content/test/webrtc_content_browsertest_base.cc
index fe151f0422f1110d9d3bb224724c24a5371e5462..d8055bf8078e34bc47170779787b4aabb09bd4cd 100644
--- a/content/test/webrtc_content_browsertest_base.cc
+++ b/content/test/webrtc_content_browsertest_base.cc
@@ -63,9 +63,8 @@ void WebRtcContentBrowserTest::AppendUseFakeUIForMediaStreamFlag() {
 std::string WebRtcContentBrowserTest::ExecuteJavascriptAndReturnResult(
     const std::string& javascript) {
   std::string result;
-  EXPECT_TRUE(ExecuteScriptAndExtractString(
-      shell()->web_contents(), javascript, &result))
-          << "Failed to execute javascript " << javascript << ".";
+  EXPECT_TRUE(ExecuteScriptAndExtractString(shell(), javascript, &result))
+      << "Failed to execute javascript " << javascript << ".";
   return result;
 }