Add missing blink files to the GN build.

Source/core/core.gyp

 #
 # Copyright (C) 2009 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 714 matching lines @@
           'link_settings': {
             'libraries': [
                '<!@(pkg-config --libs ipp|sed s/-L//)/libipps_l.a',
                '<!@(pkg-config --libs ipp|sed s/-L//)/libippcore_l.a',
             ]
           },
         }],
       ],
     },
     {
+      # GN version: //third_party/WebKit/Source/core:testing
       'target_name': 'webcore_testing',
       'type': 'static_library',
       'dependencies': [
         '../config.gyp:config',
         'webcore',
       ],
       'defines': [
         'BLINK_IMPLEMENTATION=1',
         'INSIDE_BLINK',
       ],
       'include_dirs': [
         '<(bindings_core_v8_dir)',  # FIXME: Remove once http://crbug.com/236119 is fixed.
         'testing',
         'testing/v8',
       ],
       'sources': [
+        # Note: file list duplicated in GN build.
         '<@(webcore_testing_files)',
         '<(bindings_core_v8_output_dir)/V8GarbageCollectedScriptWrappable.cpp',
         '<(bindings_core_v8_output_dir)/V8GarbageCollectedScriptWrappable.h',
         '<(bindings_core_v8_output_dir)/V8GCObservation.cpp',
         '<(bindings_core_v8_output_dir)/V8GCObservation.h',
         '<(bindings_core_v8_output_dir)/V8MallocStatistics.cpp',
         '<(bindings_core_v8_output_dir)/V8MallocStatistics.h',
         '<(bindings_core_v8_output_dir)/V8PrivateScriptTest.cpp',
         '<(bindings_core_v8_output_dir)/V8PrivateScriptTest.h',
         '<(bindings_core_v8_output_dir)/V8TypeConversions.cpp',
@@ skipping 14 matching lines @@
         '<(bindings_core_v8_output_dir)/V8LayerRectList.h',
         '<(bindings_core_v8_output_dir)/V8RefCountedScriptWrappable.cpp',
         '<(bindings_core_v8_output_dir)/V8RefCountedScriptWrappable.h',
       ],
       'sources/': [
         ['exclude', 'testing/js'],
       ],
     },
   ],  # targets
 }