New TimeToFirstURLJob* navigation metrics now work with PlzNavigate.

content/browser/loader/navigation_url_loader_impl_core.h

Index: content/browser/loader/navigation_url_loader_impl_core.h
diff --git a/content/browser/loader/navigation_url_loader_impl_core.h b/content/browser/loader/navigation_url_loader_impl_core.h
index f31d3ccbdc3f2aa7ce4800da5c4245893f1ef361..f39171804b6edd212a334ee9dda719ac4846b0c5 100644
--- a/content/browser/loader/navigation_url_loader_impl_core.h
+++ b/content/browser/loader/navigation_url_loader_impl_core.h
@@ -9,6 +9,7 @@
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
+#include "base/time/time.h"
 #include "content/browser/loader/navigation_url_loader_impl.h"
 
 namespace net {
@@ -63,6 +64,10 @@ class NavigationURLLoaderImplCore {
   // Notifies |loader_| on the UI thread that the request failed.
   void NotifyRequestFailed(int net_error);
 
+  // Notifies |loader_| on the UI thread that a begin navigation request has
+  // just been handled, before its potential first network request was made.
+  void NavigationRequested(base::TimeTicks timestamp);
+
  private:
   base::WeakPtr<NavigationURLLoaderImpl> loader_;
   NavigationResourceHandler* resource_handler_;