[NoStatePrefetch] Do not send responses to renderer in prefetch mode.

content/browser/loader/resource_dispatcher_host_impl.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.
 
 // See http://dev.chromium.org/developers/design-documents/multi-process-resource-loading
 
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
 
 #include <stddef.h>
 
@@ skipping 1620 matching lines @@
       handler.reset(new AsyncResourceHandler(request, this));
     }
 
     // The RedirectToFileResourceHandler depends on being next in the chain.
     if (request_data.download_to_file) {
       handler.reset(
           new RedirectToFileResourceHandler(std::move(handler), request));
     }
   }
 
+  // In prefetch mode, only let the main resource go through.
+  bool start_detached = request_data.is_prefetch_only &&

[mmenke, 2016/08/23 15:11:41]

|is_prefetch_only| seems confusing, given that we also have
RESOURCE_TYPE_PREFETCH, which also seems to indicate a request is only a
prefetch.  I guess we can't just make a new resource type, since we want to get
the accept header right, which is set based on the resource type, but I think we
at least need to switch to different terminology.

|do_not_send_to_renderer|?  |download_to_[network_]cache_only|?

+                        request_data.resource_type != RESOURCE_TYPE_MAIN_FRAME;

[mmenke, 2016/08/23 15:11:42]

I'm not a fan of this MAIN_FRAME logic here.  Perhaps it should be in the
renderer, based on the main frame being one of the new prerender types?

+
   // Prefetches and <a ping> requests outlive their child process.
-  if (!sync_result && IsDetachableResourceType(request_data.resource_type)) {
+  if (!sync_result && (start_detached ||
+                       IsDetachableResourceType(request_data.resource_type))) {
     handler.reset(new DetachableResourceHandler(
         request,
         base::TimeDelta::FromMilliseconds(kDefaultDetachableCancelDelayMs),
-        std::move(handler)));
+        start_detached ? nullptr : std::move(handler)));

[mmenke, 2016/08/23 15:11:41]

We need to tell the renderer the request was aborted.  Otherwise, it will keep
on waiting for a response.  We should have a unit test for this (And it should
also make sure the entire resource is read).

[mmenke, 2016/08/23 15:11:42]

Could you update the DetachableResourceHandler docs to mention this works?

   }
 
   // PlzNavigate: If using --enable-browser-side-navigation, the
   // CrossSiteResourceHandler is not needed. This codepath is not used for the
   // actual navigation request, but only the subsequent blob URL load. This does
   // not require request transfers.
   if (!IsBrowserSideNavigationEnabled()) {
     // Install a CrossSiteResourceHandler for all main frame requests. This will
     // check whether a transfer is required and, if so, pause for the UI thread
     // to drive the transfer.
@@ skipping 976 matching lines @@
   load_flags |= net::LOAD_VERIFY_EV_CERT;
   if (request_data.resource_type == RESOURCE_TYPE_MAIN_FRAME) {
     load_flags |= net::LOAD_MAIN_FRAME;
   } else if (request_data.resource_type == RESOURCE_TYPE_PREFETCH) {
     load_flags |= net::LOAD_PREFETCH;
   }
 
   if (is_sync_load)
     load_flags |= net::LOAD_IGNORE_LIMITS;
 
+  if (request_data.is_prefetch_only)
+    load_flags |= net::LOAD_PREFETCH;
+
   return load_flags;
 }
 
 void ResourceDispatcherHostImpl::UpdateResponseCertificateForTransfer(
     ResourceResponse* response,
     const net::SSLInfo& ssl_info,
     int child_id) {
   if (!ssl_info.cert)
     return;
   SSLStatus ssl;
@@ skipping 66 matching lines @@
                        << iter->filesystem_url().spec();
           return false;
         }
       }
     }
   }
   return true;
 }
 
 }  // namespace content