Convert NavigationMetricsRecorder to use the new navigation callbacks.

content/public/browser/navigation_handle.h

Index: content/public/browser/navigation_handle.h
diff --git a/content/public/browser/navigation_handle.h b/content/public/browser/navigation_handle.h
index 153be328985bbcec83b244a096998778cc72d4a5..253fb933523b27f20235ba3e0db2579b77c08ed9 100644
--- a/content/public/browser/navigation_handle.h
+++ b/content/public/browser/navigation_handle.h
@@ -176,6 +176,10 @@ class CONTENT_EXPORT NavigationHandle {
   // GetNetErrorCode will be net::OK.
   virtual bool IsErrorPage() = 0;
 
+  // The previous main frame URL that the user was on. This may be empty if
+  // there was no last committed entry.
+  virtual const GURL& GetPreviousURL() = 0;
+
   // Returns the response headers for the request, or nullptr if there aren't
   // any response headers or they have not been received yet. The response
   // headers may change during the navigation (e.g. after encountering a server