Fix Performance::now() for browser navigations.

Source/core/loader/DocumentLoadTiming.cpp

 /*
  * Copyright (C) 2011 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 56 matching lines @@
 {
     ASSERT(!m_navigationStart && !m_referenceMonotonicTime && !m_referenceWallTime);
 
     m_navigationStart = m_referenceMonotonicTime = monotonicallyIncreasingTime();
     m_referenceWallTime = currentTime();
 }
 
 void DocumentLoadTiming::setNavigationStart(double navigationStart)
 {
     ASSERT(m_referenceMonotonicTime && m_referenceWallTime);
+
+    // This should be used only to indicate that the navigation started in the
+    // embedder before the renderer was created.
+    ASSERT(navigationStart <= m_navigationStart);
     m_navigationStart = navigationStart;
+
+    // |m_referenceMonotonicTime| and |m_referenceWallTime| represent
+    // navigationStart. When the embedder sets navigationStart (because the
+    // navigation started earlied on the browser side), we need to adjust these
+    // as well.
+    m_referenceWallTime = monotonicTimeToPseudoWallTime(navigationStart);
+    m_referenceMonotonicTime = navigationStart;
 }
 
 void DocumentLoadTiming::addRedirect(const KURL& redirectingUrl, const KURL& redirectedUrl)
 {
     m_redirectCount++;
     if (!m_redirectStart)
         m_redirectStart = m_fetchStart;
     m_redirectEnd = m_fetchStart = monotonicallyIncreasingTime();
     // Check if the redirected url is allowed to access the redirecting url's timing information.
     RefPtr<SecurityOrigin> redirectedSecurityOrigin = SecurityOrigin::create(redirectedUrl);
     m_hasCrossOriginRedirect = !redirectedSecurityOrigin->canRequest(redirectingUrl);
 }
 
 } // namespace WebCore