[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));
     }
   }
 
+  const bool detached =

[mmenke, 2016/08/22 14:08:23]

style:  const is generally not used for stack variables that aren't compile-time
constants.

+      delegate()->ShouldSinkResponse(request, request_data.resource_type);

[mmenke, 2016/08/22 14:08:23]

sink / detach:  Should use consistent naming.

+
   // Prefetches and <a ping> requests outlive their child process.
-  if (!sync_result && IsDetachableResourceType(request_data.resource_type)) {
+  if (detached ||
+      (!sync_result && IsDetachableResourceType(request_data.resource_type))) {

[mmenke, 2016/08/22 14:08:22]

Should we instead introduce a resource type for this instead?

[mmenke, 2016/08/22 14:08:23]

BUG:  The sync_result check should cover the case detached is true - we don't
want to let the embedder cause the entire renderer to hang, no matter how much
it may want to.

[mmenke, 2016/08/22 14:11:00]

Moreover, do we really want the embedder controlling behavior here?  The new
magic prerender type has logic in content/, so I assume content or blink knows
that this is a not a real navigation, and the renderer doesn't really need the
data.  So it doesn't seem like the embedder should be controlling this.

     handler.reset(new DetachableResourceHandler(
         request,
         base::TimeDelta::FromMilliseconds(kDefaultDetachableCancelDelayMs),
-        std::move(handler)));
+        detached ? nullptr : std::move(handler)));
   }
 
   // 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 1062 matching lines @@
                        << iter->filesystem_url().spec();
           return false;
         }
       }
     }
   }
   return true;
 }
 
 }  // namespace content