Files services library: Add an "output stream" file impl helper class.

mojo/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/module_args/mojo.gni")
 import("//mojo/public/mojo.gni")
 
 group("mojo") {
   # Meta-target, don't link into production code.
   testonly = true
@@ skipping 42 matching lines @@
     "//mojo/edk/system:tests",
     "//mojo/edk/test:public_tests",
     "//mojo/dart/embedder/test:dart_unittests",
     "//mojo/public/cpp/bindings/tests:versioning_apptests",
     "//mojo/services/view_manager/public/cpp/tests:mojo_view_manager_lib_unittests",
     "//mojo/tests:mojo_task_tracker_perftests",
     "//mojo/tools:message_generator",
     "//mojo/gles2:mgl_unittests",
     "//mojo/gpu:apptests",
     "//mojo/services/files/public/c:apptests",
+    "//mojo/services/files/public/cpp:files_impl_apptests",
   ]
 
   if (is_linux || is_android) {
     deps += [ "//mojo/converters/surfaces/tests:mojo_surfaces_lib_unittests" ]
   }
 
   # TODO(jamesr): We only support building V8 snapshot data on a linux host since it
   # needs a 32 bit toolchain and we don't have one configured for mac hosts.
   if (host_os == "linux") {
     deps += [ "//mojo/edk/js:tests" ]
   }
 
   if (mojo_use_prebuilt_network_service) {
     deps += [ "//mojo/public/tools:copy_network_service_apptests" ]
   }
 }