Revert of Fix Performance::now() for browser navigations.

Source/core/loader/DocumentLoadTiming.cpp

Index: Source/core/loader/DocumentLoadTiming.cpp
diff --git a/Source/core/loader/DocumentLoadTiming.cpp b/Source/core/loader/DocumentLoadTiming.cpp
index 3d7edd2a1d51f8d0da6532b220d9df9f677c5750..6204ca613575cfa5214b40a644c225e5ac9384de 100644
--- a/Source/core/loader/DocumentLoadTiming.cpp
+++ b/Source/core/loader/DocumentLoadTiming.cpp
@@ -74,18 +74,7 @@
 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)