Add page load metrics for no-store forward back navigations.

content/browser/frame_host/navigation_handle_impl.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 "content/browser/frame_host/navigation_handle_impl.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "content/browser/devtools/render_frame_devtools_agent_host.h"
@@ skipping 188 matching lines @@
 }
 
 bool NavigationHandleImpl::IsSamePage() {
   DCHECK(state_ == DID_COMMIT || state_ == DID_COMMIT_ERROR_PAGE)
       << "This accessor should not be called before the navigation has "
          "committed.";
   return is_same_page_;
 }
 
 const net::HttpResponseHeaders* NavigationHandleImpl::GetResponseHeaders() {
-   return response_headers_.get();
+  DCHECK_GE(state_, WILL_REDIRECT_REQUEST);
+  return response_headers_.get();
 }
 
 bool NavigationHandleImpl::HasCommitted() {
   return state_ == DID_COMMIT || state_ == DID_COMMIT_ERROR_PAGE;
 }
 
 bool NavigationHandleImpl::IsErrorPage() {
   return state_ == DID_COMMIT_ERROR_PAGE;
 }
 
@@ skipping 337 matching lines @@
                       throttles_to_register.end());
     throttles_to_register.weak_clear();
   }
   std::unique_ptr<NavigationThrottle> devtools_throttle =
       RenderFrameDevToolsAgentHost::CreateThrottleForNavigation(this);
   if (devtools_throttle)
     throttles_.push_back(devtools_throttle.release());
 }
 
 }  // namespace content