Add a NavigationThrottle to the public content/ interface

content/browser/web_contents/web_contents_impl.cc

 // Copyright (c) 2012 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 "content/browser/web_contents/web_contents_impl.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
@@ skipping 2760 matching lines @@
     return true;
   return delegate_ && delegate_->ShouldFocusLocationBarByDefault(this);
 }
 
 void WebContentsImpl::SetFocusToLocationBar(bool select_all) {
   if (delegate_)
     delegate_->SetFocusToLocationBar(select_all);
 }
 
 void WebContentsImpl::DidStartNavigation(NavigationHandle* navigation_handle) {
+  static_cast<NavigationHandleImpl*>(navigation_handle)->set_web_contents(this);

[nasko, 2015/09/14 22:00:04]

Is this the only usage of set_web_contents? Can we avoid having this settable
through a public method if noone else needs it?

[clamy, 2015/09/14 22:12:10]

Well if I have a handy way to get to the WebContents from somewhere inside
/frame_host yes, otherwise that requires making WebContentsImpl a friend of
NavigationHandleImpl.

[Charlie Reis, 2015/09/16 00:09:24]

Yeah, this is one of the tricky aspects of having frame_host code know about
WebContents.  I see that it's needed, though, since NavigationHandle really is
tied to WebContentsObserver.  Not sure if I see a better way to handle it than
this.

   FOR_EACH_OBSERVER(WebContentsObserver, observers_,
                     DidStartNavigation(navigation_handle));
 }
 
 void WebContentsImpl::DidRedirectNavigation(
     NavigationHandle* navigation_handle) {
   FOR_EACH_OBSERVER(WebContentsObserver, observers_,
                     DidRedirectNavigation(navigation_handle));
 }
 
@@ skipping 1836 matching lines @@
   return NULL;
 }
 
 void WebContentsImpl::SetForceDisableOverscrollContent(bool force_disable) {
   force_disable_overscroll_content_ = force_disable;
   if (view_)
     view_->SetOverscrollControllerEnabled(CanOverscrollContent());
 }
 
 }  // namespace content