Revert the merge of CrossSiteResourceHandler and NavigationResourceThrottle.

content/browser/devtools/render_frame_devtools_agent_host.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/devtools/render_frame_devtools_agent_host.h"
 
 #include <tuple>
 #include <utility>
 
 #include "base/guid.h"
@@ skipping 551 matching lines @@
 RenderFrameDevToolsAgentHost::~RenderFrameDevToolsAgentHost() {
   Instances::iterator it = std::find(g_instances.Get().begin(),
                                      g_instances.Get().end(),
                                      this);
   if (it != g_instances.Get().end())
     g_instances.Get().erase(it);
 }
 
 void RenderFrameDevToolsAgentHost::ReadyToCommitNavigation(
     NavigationHandle* navigation_handle) {
-  // TODO(clamy): Switch RenderFrameDevToolsAgentHost to always buffer messages
-  // until ReadyToCommitNavigation is called, now that it is also called in
-  // non-PlzNavigate mode.
-  if (!IsBrowserSideNavigationEnabled())
-    return;
+  // ReadyToCommitNavigation should only be called in PlzNavigate.
+  DCHECK(IsBrowserSideNavigationEnabled());
 
   // If the navigation is not tracked, return;
   if (navigating_handles_.count(navigation_handle) == 0)
     return;
 
   RenderFrameHostImpl* render_frame_host_impl =
       static_cast<RenderFrameHostImpl*>(
           navigation_handle->GetRenderFrameHost());
   if (current_->host() != render_frame_host_impl || current_frame_crashed_) {
     SetPending(render_frame_host_impl);
@@ skipping 486 matching lines @@
     RenderFrameHost* host) {
   return (current_ && current_->host() == host) ||
       (pending_ && pending_->host() == host);
 }
 
 bool RenderFrameDevToolsAgentHost::IsChildFrame() {
   return current_ && current_->host()->GetParent();
 }
 
 }  // namespace content