Correctly record and pass around navigation start time.

components/web_view/navigation_entry.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/web_view/navigation_entry.h"
 
 namespace web_view {
 
 NavigationEntry::NavigationEntry(mojo::URLRequestPtr original_request)
     : url_request_(original_request.Pass()) {}
 
 NavigationEntry::NavigationEntry(const GURL& raw_url)
     : url_request_(raw_url) {}
 
 NavigationEntry::~NavigationEntry() {}
 
-mojo::URLRequestPtr NavigationEntry::BuildURLRequest() const {
+mojo::URLRequestPtr NavigationEntry::BuildURLRequest() {
   return url_request_.Clone();
 }
 
 }  // namespace web_view