Created a DownloadManager interface, for use in unit tests..

content/content_tests.gypi

 # Copyright (c) 2011 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': [
     {
       'target_name': 'test_support_content',
       'type': 'static_library',
       'defines!': ['CONTENT_IMPLEMENTATION'],
       'dependencies': [
         '../build/temp_gyp/googleurl.gyp:googleurl',
         'content_common',
         '../skia/skia.gyp:skia',
         '../testing/gmock.gyp:gmock',
         '../testing/gtest.gyp:gtest',
         '../third_party/WebKit/Source/WebKit/chromium/WebKit.gyp:webkit',
         '../ui/gfx/compositor/compositor.gyp:test_compositor',
         '../ui/gfx/surface/surface.gyp:surface',
         '../ui/ui.gyp:ui_test_support',
         '../webkit/support/webkit_support.gyp:appcache',
       ],
       'include_dirs': [
         '..',
       ],
       'sources': [
         # TODO(phajdan.jr): All of those files should live in content/test.
+        'browser/download/mock_download_manager.cc',
         'browser/download/mock_download_manager.h',
         'browser/download/mock_download_manager_delegate.cc',
         'browser/download/mock_download_manager_delegate.h',
         'browser/geolocation/arbitrator_dependency_factories_for_test.cc',
         'browser/geolocation/arbitrator_dependency_factories_for_test.h',
         'browser/geolocation/fake_access_token_store.cc',
         'browser/geolocation/fake_access_token_store.h',
         'browser/geolocation/mock_location_provider.cc',
         'browser/geolocation/mock_location_provider.h',
         'browser/mock_content_browser_client.cc',
@@ skipping 308 matching lines @@
           ],
           'sources': [
             'common/gpu/media/omx_video_decode_accelerator_unittest.cc',
           ],
         }
       ],
     },
    ],
   ],
 }