prerender: Don't set the priority to net::IDLE on Android.

chrome/browser/loader/chrome_resource_dispatcher_host_delegate.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 "chrome/browser/loader/chrome_resource_dispatcher_host_delegate.h"
 
 #include <stdint.h>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 403 matching lines @@
 
 void ChromeResourceDispatcherHostDelegate::RequestBeginning(
     net::URLRequest* request,
     content::ResourceContext* resource_context,
     content::AppCacheService* appcache_service,
     ResourceType resource_type,
     ScopedVector<content::ResourceThrottle>* throttles) {
   if (safe_browsing_.get())
     safe_browsing_->OnResourceRequest(request);
 
+// The lowering of request priority causes issues with scheduling, since
+// content::ResourceScheduler uses it to delay and throttle requests. This is
+// disabled only on Android, as the prerenders are not likely to compete wuth

[droger, 2016/10/07 09:08:23]

s/wuth/with/

[Benoit L, 2016/10/07 09:27:35]

Done.

+// page loads there.
+// See https://crbug.com/652746 for details.
+// TODO(lizeb,droger): Remove this hack, and fix the issue on all platforms.

[droger, 2016/10/07 09:08:23]

Nit:

We're not quite sure that this is really a hack, it may be the right fix for all
platforms.
I would drop the first part of the comment and just put:

// TODO(lizeb,droger): Fix the issue on all platforms.

[Benoit L, 2016/10/07 09:27:35]

Done.

+#if !defined(OS_ANDROID)
   const ResourceRequestInfo* info = ResourceRequestInfo::ForRequest(request);
   bool is_prerendering =
       info->GetVisibilityState() == blink::WebPageVisibilityStatePrerender;
   if (is_prerendering) {
     // Requests with the IGNORE_LIMITS flag set (i.e., sync XHRs)
     // should remain at MAXIMUM_PRIORITY.
     if (request->load_flags() & net::LOAD_IGNORE_LIMITS) {
       DCHECK_EQ(request->priority(), net::MAXIMUM_PRIORITY);
     } else {
       request->SetPriority(net::IDLE);
     }
   }
+#endif  // OS_ANDROID
 
   ProfileIOData* io_data = ProfileIOData::FromResourceContext(
       resource_context);
 
 #if defined(OS_ANDROID)
   if (resource_type != content::RESOURCE_TYPE_MAIN_FRAME)
     InterceptNavigationDelegate::UpdateUserGestureCarryoverInfo(request);
 #endif
 
 #if defined(OS_CHROMEOS)
@@ skipping 29 matching lines @@
 
   signin::FixMirrorRequestHeaderHelper(request, GURL() /* redirect_url */,
                                        io_data, info->GetChildID(),
                                        info->GetRouteID());
 
   AppendStandardResourceThrottles(request,
                                   resource_context,
                                   resource_type,
                                   throttles);
 #if !defined(DISABLE_NACL)
   if (!is_prerendering) {

[droger, 2016/10/07 09:08:23]

FYI:
|is_prerendering| is used here, compile might fail if NACL gets enabled on
android somehow.

Not sure this can ever be a problem though.

[Benoit L, 2016/10/07 09:27:35]

Done.

     AppendComponentUpdaterThrottles(request,
                                     resource_context,
                                     resource_type,
                                     throttles);
   }
 #endif
 
   if (io_data->resource_prefetch_predictor_observer()) {
     io_data->resource_prefetch_predictor_observer()->OnRequestStarted(
         request, resource_type, info->GetChildID(), info->GetRenderFrameID());
@@ skipping 365 matching lines @@
           base::Bind(&ChromeResourceDispatcherHostDelegate::OnAbortedFrameLoad,
                     base::Unretained(this), url, request_loading_time));
       return;
   }
 
   std::string metric_name = (request_loading_time.InMilliseconds() < 100 ?
       "Net.ErrAborted.Fast" : "Net.ErrAborted.Slow");
   rappor::SampleDomainAndRegistryFromGURL(
       g_browser_process->rappor_service(), metric_name, url);
 }