Add an utility interface ReaderProxy and its implementation for local file.

chrome/chrome_tests_unit.gypi

 # Copyright 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.
 {
   'targets': [
     {
       # This target contains mocks and test utilities that don't belong in
       # production libraries but are used by more than one test executable.
       'target_name': 'test_support_common',
       'type': 'static_library',
@@ skipping 536 matching lines @@
         'browser/chromeos/customization_document_unittest.cc',
         'browser/chromeos/dbus/cros_dbus_service_unittest.cc',
         'browser/chromeos/dbus/printer_service_provider_unittest.cc',
         'browser/chromeos/dbus/proxy_resolution_service_provider_unittest.cc',
         'browser/chromeos/dbus/service_provider_test_helper.cc',
         'browser/chromeos/dbus/service_provider_test_helper.h',
         'browser/chromeos/display/display_preferences_unittest.cc',
         'browser/chromeos/drive/drive_cache_metadata_unittest.cc',
         'browser/chromeos/drive/drive_cache_unittest.cc',
         'browser/chromeos/drive/drive_download_handler_unittest.cc',
+        'browser/chromeos/drive/drive_file_stream_reader_unittest.cc',
         'browser/chromeos/drive/drive_file_system_unittest.cc',
         'browser/chromeos/drive/drive_file_system_util_unittest.cc',
         'browser/chromeos/drive/drive_prefetcher_unittest.cc',
         'browser/chromeos/drive/drive_resource_metadata_storage_unittest.cc',
         'browser/chromeos/drive/drive_resource_metadata_unittest.cc',
         'browser/chromeos/drive/drive_scheduler_unittest.cc',
         'browser/chromeos/drive/drive_sync_client_unittest.cc',
         'browser/chromeos/drive/drive_system_service_unittest.cc',
         'browser/chromeos/drive/drive_test_util.cc',
         'browser/chromeos/drive/drive_test_util.h',
@@ skipping 1853 matching lines @@
               # more details.
               'DebugInformationFormat': '3',
               'ProgramDataBaseFileName': '<(PRODUCT_DIR)/unit_tests.exe.pdb',
             },
           },
         },
       ],
     }],
   ],  # 'conditions'
 }