add a flag to enable/disable download interception on android

chrome/browser/renderer_host/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/renderer_host/chrome_resource_dispatcher_host_delegate.h"
 
 #include <stdint.h>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 400 matching lines @@
       base::Bind(&NotifyDownloadInitiatedOnUI, child_id, route_id));
 
   // If it's from the web, we don't trust it, so we push the throttle on.
   if (is_content_initiated) {
     const content::ResourceRequestInfo* info =
         content::ResourceRequestInfo::ForRequest(request);
     throttles->push_back(new DownloadResourceThrottle(
         download_request_limiter_, info->GetWebContentsGetterForRequest(),
         request->url(), request->method()));
 #if BUILDFLAG(ANDROID_JAVA_UI)
-    throttles->push_back(
-        new chrome::InterceptDownloadResourceThrottle(
-            request, child_id, route_id, request_id));
+    if (chrome::InterceptDownloadResourceThrottle::

[svaldez, 2016/02/12 15:21:19]

Consider getting rid of the check here, and instead having
InterceptDownloadResourceThrottle check the IsDownloadInterceptionEnabled and do
nothing if so.

This lets us keep our metrics from InterceptDownloadResourceThrottle.

[qinmin, 2016/02/12 17:27:00]

Done. However, there is a very tiny performance hit as we always need to go
through the throttle for each download.

+        IsDownloadInterceptionEnabled()) {
+      throttles->push_back(new chrome::InterceptDownloadResourceThrottle(
+          request, child_id, route_id, request_id));
+    }
 #endif
   }
 
   // If this isn't a new request, we've seen this before and added the standard
   //  resource throttles already so no need to add it again.
   if (!request->is_pending()) {
     AppendStandardResourceThrottles(request,
                                     resource_context,
                                     content::RESOURCE_TYPE_MAIN_FRAME,
                                     throttles);
@@ skipping 295 matching lines @@
     return data_reduction_proxy_io_data->ShouldEnableLoFiMode(url_request);
   return false;
 }
 
 // static
 void ChromeResourceDispatcherHostDelegate::
     SetExternalProtocolHandlerDelegateForTesting(
     ExternalProtocolHandler::Delegate* delegate) {
   g_external_protocol_handler_delegate = delegate;
 }