Implement prefetching in chrome

chrome/browser/renderer_host/resource_dispatcher_host.cc

 // Copyright (c) 2010 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.
 
 // See http://dev.chromium.org/developers/design-documents/multi-process-resource-loading
 
 #include "chrome/browser/renderer_host/resource_dispatcher_host.h"
 
 #include <vector>
 
@@ skipping 107 matching lines @@
 // Consults the RendererSecurity policy to determine whether the
 // ResourceDispatcherHost should service this request.  A request might be
 // disallowed if the renderer is not authorized to retrieve the request URL or
 // if the renderer is attempting to upload an unauthorized file.
 bool ShouldServiceRequest(ChildProcessInfo::ProcessType process_type,
                           int child_id,
                           const ViewHostMsg_Resource_Request& request_data)  {
   if (process_type == ChildProcessInfo::PLUGIN_PROCESS)
     return true;
 
+  if (request_data.resource_type == ResourceType::PREFETCH &&
+      CommandLine::ForCurrentProcess()->HasSwitch(switches::kDisablePrefetch))
+    return false;
+
   ChildProcessSecurityPolicy* policy =
       ChildProcessSecurityPolicy::GetInstance();
 
   // Check if the renderer is permitted to request the requested URL.
   if (!policy->CanRequestURL(child_id, request_data.url)) {
     LOG(INFO) << "Denied unauthorized request for " <<
         request_data.url.possibly_invalid_spec();
     return false;
   }
 
@@ skipping 1692 matching lines @@
     // blocking stylesheets, scripts and fonts, but are higher priority than
     // images because if they exist they are probably more central to the page
     // focus than images on the page.
     case ResourceType::SUB_RESOURCE:
     case ResourceType::OBJECT:
     case ResourceType::MEDIA:
     case ResourceType::WORKER:
     case ResourceType::SHARED_WORKER:
       return net::LOW;
 
-    // Images are the lowest priority because they typically do not block
+    // Images are the "lowest" priority because they typically do not block
     // downloads or rendering and most pages have some useful content without
     // them.
     case ResourceType::IMAGE:
       return net::LOWEST;
 
+    // Prefetches are at a lower priority than even LOWEST, since they
+    // are not even required for rendering of the current page.
+    case ResourceType::PREFETCH:
+      return net::IDLE;
+
     default:
       // When new resource types are added, their priority must be considered.
       NOTREACHED();
       return net::LOW;
   }
 }