Make ResourceHandler::OnWillRead able to complete asynchronously.

content/test/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
@@ skipping 1121 matching lines @@
     "../browser/indexed_db/mock_indexed_db_callbacks.cc",
     "../browser/indexed_db/mock_indexed_db_callbacks.h",
     "../browser/indexed_db/mock_indexed_db_database_callbacks.cc",
     "../browser/indexed_db/mock_indexed_db_database_callbacks.h",
     "../browser/indexed_db/mock_indexed_db_factory.cc",
     "../browser/indexed_db/mock_indexed_db_factory.h",
     "../browser/leveldb_wrapper_impl_unittest.cc",
     "../browser/loader/async_resource_handler_unittest.cc",
     "../browser/loader/async_revalidation_driver_unittest.cc",
     "../browser/loader/async_revalidation_manager_unittest.cc",
+    "../browser/loader/detachable_resource_handler_unittest.cc",
     "../browser/loader/intercepting_resource_handler_unittest.cc",
     "../browser/loader/mime_sniffing_resource_handler_unittest.cc",
     "../browser/loader/mock_resource_loader.cc",
     "../browser/loader/mock_resource_loader.h",
     "../browser/loader/mojo_async_resource_handler_unittest.cc",
     "../browser/loader/navigation_url_loader_unittest.cc",
     "../browser/loader/netlog_observer_unittest.cc",
     "../browser/loader/redirect_to_file_resource_handler_unittest.cc",
     "../browser/loader/resource_buffer_unittest.cc",
     "../browser/loader/resource_dispatcher_host_unittest.cc",
@@ skipping 678 matching lines @@
   if (is_android) {
     deps += [ "//testing/android/native_test:native_test_native_code" ]
   }
 }
 
 group("fuzzers") {
   deps = [
     "//content/test/fuzzer",
   ]
 }