Use WebViewHelper::LocalMainFrame where possible.

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

 /*
  * Copyright (C) 2017 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 106 matching lines @@
     String file_path("frameserialization/" + file_name);
     RegisterMockedFileURLLoad(parsed_url, file_path, "text/html");
     FrameTestHelpers::LoadFrame(MainFrameImpl(), url.Utf8().data());
     SingleLinkRewritingDelegate delegate(parsed_url, WebString("local"));
     SimpleWebFrameSerializerClient serializer_client;
     WebFrameSerializer::Serialize(MainFrameImpl(), &serializer_client,
                                   &delegate);
     return serializer_client.ToString();
   }
 
-  WebLocalFrameBase* MainFrameImpl() {
-    return helper_.WebView()->MainFrameImpl();
-  }
+  WebLocalFrameBase* MainFrameImpl() { return helper_.LocalMainFrame(); }
 
  private:
   FrameTestHelpers::WebViewHelper helper_;
 };
 
 TEST_F(WebFrameSerializerTest, URLAttributeValues) {
   RegisterMockedImageURLLoad("javascript:\"");
 
   const char* expected_html =
       "\n<!-- saved from url=(0020)http://www.test.com/ -->\n"
@@ skipping 27 matching lines @@
 }
 
 TEST_F(WebFrameSerializerTest, FromUrlWithMinusMinus) {
   String actual_html =
       SerializeFile("http://www.test.com?--x--", "text_only_page.html");
   EXPECT_EQ("<!-- saved from url=(0030)http://www.test.com/?-%2Dx-%2D -->",
             actual_html.Substring(1, 60));
 }
 
 }  // namespace blink