Do not sniff mime type for fetch() requests

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 1697 matching lines @@
 
   // Add the post mime sniffing throttles.
   handler.reset(new ThrottlingResourceHandler(
       std::move(handler), request, std::move(post_mime_sniffing_throttles)));
 
   PluginService* plugin_service = nullptr;
 #if defined(ENABLE_PLUGINS)
   plugin_service = PluginService::GetInstance();
 #endif
 
-  // Insert a buffered event handler to sniff the mime type.
-  // Note: all ResourceHandler following the MimeSniffingResourceHandler should
-  // expect OnWillRead to be called *before* OnResponseStarted as part of the
-  // mime sniffing process.
-  handler.reset(new MimeSniffingResourceHandler(
-      std::move(handler), this, plugin_service, intercepting_handler, request));
+  if (fetch_request_context_type != REQUEST_CONTEXT_TYPE_FETCH) {
+    // fetch() ignores mime sniffing.

[tyoshino (SeeGerritForStatus), 2016/09/08 06:04:31]

place above the if

[yhirano, 2016/09/08 06:08:39]

Done.

+    //
+    // Insert a buffered event handler to sniff the mime type.
+    // Note: all ResourceHandler following the MimeSniffingResourceHandler
+    // should expect OnWillRead to be called *before* OnResponseStarted as
+    // part of the mime sniffing process.
+    handler.reset(new MimeSniffingResourceHandler(
+        std::move(handler), this, plugin_service, intercepting_handler,
+        request));
+  }
 
   // Add the pre mime sniffing throttles.
   handler.reset(new ThrottlingResourceHandler(
       std::move(handler), request, std::move(pre_mime_sniffing_throttles)));
 
   return handler;
 }
 
 void ResourceDispatcherHostImpl::OnReleaseDownloadedFile(int request_id) {
   UnregisterDownloadedTempFile(filter_->child_id(), request_id);
@@ skipping 996 matching lines @@
         request_info->GetRouteID(), is_content_initiated, true, &throttles);
     if (!throttles.empty()) {
       handler.reset(new ThrottlingResourceHandler(std::move(handler), request,
                                                   std::move(throttles)));
     }
   }
   return handler;
 }
 
 }  // namespace content