Adds test coverage for 521663

Source/web/tests/WebFrameTest.cpp

 /*
  * Copyright (C) 2010 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 7025 matching lines @@
     FrameTestHelpers::loadFrame(localFrame, m_baseURL + "subframe-hello.html");
     std::string content = localFrame->contentAsText(1024).utf8();
     EXPECT_EQ("hello", content);
 
     // Manually reset to break WebViewHelper's dependency on the stack allocated
     // TestWebFrameClient.
     reset();
     remoteFrame->close();
 }
 
+namespace {
+
+class SwapMainFrameWhenTitleChangesWebFrameClient : public FrameTestHelpers::TestWebFrameClient {
+public:
+    SwapMainFrameWhenTitleChangesWebFrameClient() {}
+    ~SwapMainFrameWhenTitleChangesWebFrameClient() override {}
+
+    void didReceiveTitle(WebLocalFrame* frame, const WebString&, WebTextDirection) override
+    {
+        if (!frame->parent())
+            frame->swap(WebRemoteFrame::create(WebTreeScopeType::Document, nullptr));
+    }
+};
+
+} // anonymous namespace
+
+TEST_F(WebFrameTest, SwapMainFrameWhileLoading)
+{
+    SwapMainFrameWhenTitleChangesWebFrameClient frameClient;
+
+    FrameTestHelpers::WebViewHelper webViewHelper;
+    registerMockedHttpURLLoad("frame-a-b-c.html");
+    registerMockedHttpURLLoad("subframe-a.html");
+    registerMockedHttpURLLoad("subframe-b.html");
+    registerMockedHttpURLLoad("subframe-c.html");
+    registerMockedHttpURLLoad("subframe-hello.html");
+
+    webViewHelper.initializeAndLoad(m_baseURL + "frame-a-b-c.html", true, &frameClient);
+}
+
 void swapAndVerifyFirstChildConsistency(const char* const message, WebFrame* parent, WebFrame* newChild)
 {
     SCOPED_TRACE(message);
     parent->firstChild()->swap(newChild);
 
     EXPECT_EQ(newChild, parent->firstChild());
     EXPECT_EQ(newChild->parent(), parent);
     EXPECT_EQ(newChild, parent->lastChild()->previousSibling()->previousSibling());
     EXPECT_EQ(newChild->nextSibling(), parent->lastChild()->previousSibling());
 }
@@ skipping 1144 matching lines @@
 
 TEST_F(WebFrameTest, MaxFramesDetach)
 {
     registerMockedHttpURLLoad("max-frames-detach.html");
     FrameTestHelpers::WebViewHelper webViewHelper;
     WebViewImpl* webViewImpl = webViewHelper.initializeAndLoad(m_baseURL + "max-frames-detach.html", true);
     webViewImpl->mainFrameImpl()->collectGarbage();
 }
 
 } // namespace blink