Pass NavigationContext to WebStateImpl::OnNavigationStarted.

ios/web/web_state/web_state_impl.mm

 // Copyright 2013 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.
 
 #import "ios/web/web_state/web_state_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/logging.h"
@@ skipping 652 matching lines @@
 }
 
 id<CRWWebViewProxy> WebStateImpl::GetWebViewProxy() const {
   return [web_controller_ webViewProxy];
 }
 
 bool WebStateImpl::HasOpener() const {
   return created_with_opener_;
 }
 
-void WebStateImpl::OnProvisionalNavigationStarted(const GURL& url) {
+void WebStateImpl::OnNavigationStarted(web::NavigationContext* context) {
+  // TODO(crbug.com/713836): pass context to WebStateObserver callback.
   for (auto& observer : observers_)
-    observer.ProvisionalNavigationStarted(url);
+    observer.ProvisionalNavigationStarted(context->GetUrl());
 }
 
 void WebStateImpl::OnNavigationFinished(web::NavigationContext* context) {
   for (auto& observer : observers_)
     observer.DidFinishNavigation(context);
 }
 
 #pragma mark - NavigationManagerDelegate implementation
 
 void WebStateImpl::GoToIndex(int index) {
@@ skipping 23 matching lines @@
     const LoadCommittedDetails& load_details) {
   for (auto& observer : observers_)
     observer.NavigationItemCommitted(load_details);
 }
 
 WebState* WebStateImpl::GetWebState() {
   return this;
 }
 
 }  // namespace web