Transmit a X-Chrome-UMA-Enabled bit to Google domains from clients that have UMA enabled.

chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.h

 // 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.
 
 #ifndef CHROME_BROWSER_RENDERER_HOST_CHROME_RESOURCE_DISPATCHER_HOST_DELEGATE_H_
 #define CHROME_BROWSER_RENDERER_HOST_CHROME_RESOURCE_DISPATCHER_HOST_DELEGATE_H_
 #pragma once
 
 #include <vector>
 
@@ skipping 69 matching lines @@
 
  private:
   void AppendStandardResourceThrottles(
       const net::URLRequest* request,
       content::ResourceContext* resource_context,
       int child_id,
       int route_id,
       ResourceType::Type resource_type,
       ScopedVector<content::ResourceThrottle>* throttles);
 
+  // Adds Chrome experiment and metrics state as custom headers to |request|.
+  // This is a best-effort attempt, and does not interrupt the request if the
+  // headers can not be appended.
+  void AppendChromeMetricsHeaders(
+      net::URLRequest* request,
+      content::ResourceContext* resource_context,
+      ResourceType::Type resource_type);
+
   scoped_refptr<DownloadRequestLimiter> download_request_limiter_;
   scoped_refptr<SafeBrowsingService> safe_browsing_;
   scoped_refptr<UserScriptListener> user_script_listener_;
   prerender::PrerenderTracker* prerender_tracker_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeResourceDispatcherHostDelegate);
 };
 
 #endif  // CHROME_BROWSER_RENDERER_HOST_CHROME_RESOURCE_DISPATCHER_HOST_DELEGATE_H_