Introduce mock test system for navigator content utils

Source/modules/modules.gypi

 {
   'variables': {
     # Experimental hooks for embedder to provide extra IDL and source files.
     #
     # Note: this is not a supported API. If you rely on this, you will be broken
     # from time to time as the code generator changes in backward incompatible
     # ways.
     'extra_blink_module_idl_files': [],
     'extra_blink_module_files': [],
     # Files for which bindings (.cpp and .h files) will be generated
@@ skipping 910 matching lines @@
       'websockets/WebSocketHandshake.cpp',
       'websockets/WebSocketHandshake.h',
       'websockets/WebSocketPerMessageDeflate.cpp',
       'websockets/WebSocketPerMessageDeflate.h',
       'websockets/WorkerThreadableWebSocketChannel.cpp',
       'websockets/WorkerThreadableWebSocketChannel.h',
     ],
     # 'partial interface' or target (right side of) 'implements'
     'modules_testing_dependency_idl_files' : [
       'geolocation/testing/InternalsGeolocation.idl',
+      'navigatorcontentutils/testing/InternalsNavigatorContentUtils.idl',
       'speech/testing/InternalsSpeechSynthesis.idl',
       'vibration/testing/InternalsVibration.idl',
     ],
     'modules_testing_files': [
       'geolocation/testing/GeolocationClientMock.cpp',
       'geolocation/testing/GeolocationClientMock.h',
       'geolocation/testing/InternalsGeolocation.cpp',
       'geolocation/testing/InternalsGeolocation.h',
+      'navigatorcontentutils/testing/InternalsNavigatorContentUtils.cpp',
+      'navigatorcontentutils/testing/InternalsNavigatorContentUtils.h',
+      'navigatorcontentutils/testing/NavigatorContentUtilsClientMock.cpp',
+      'navigatorcontentutils/testing/NavigatorContentUtilsClientMock.h',
       'speech/testing/InternalsSpeechSynthesis.cpp',
       'speech/testing/InternalsSpeechSynthesis.h',
       'speech/testing/PlatformSpeechSynthesizerMock.cpp',
       'speech/testing/PlatformSpeechSynthesizerMock.h',
       'vibration/testing/InternalsVibration.cpp',
       'vibration/testing/InternalsVibration.h',
     ],
     'modules_unittest_files': [
       'indexeddb/IDBKeyPathTest.cpp',
       'indexeddb/IDBRequestTest.cpp',
       'indexeddb/IDBTransactionTest.cpp',
       'websockets/WebSocketDeflaterTest.cpp',
       'websockets/WebSocketExtensionDispatcherTest.cpp',
       'websockets/WebSocketExtensionParserTest.cpp',
       'websockets/WebSocketPerMessageDeflateTest.cpp',
     ],
   },
 }