Delete unused WebViewBenchmarkSupport interface

Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'ApplicationCacheHost.cpp',
       'ApplicationCacheHostInternal.h',
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'AsyncFileSystemChromium.cpp',
       'AsyncFileSystemChromium.h',
@@ skipping 236 matching lines @@
       'WebSurroundingText.cpp',
       'WebTextCheckingCompletionImpl.cpp',
       'WebTextCheckingCompletionImpl.h',
       'WebTextCheckingResult.cpp',
       'WebTextInputInfo.cpp',
       'WebTextRun.cpp',
       'WebURLLoadTiming.cpp',
       'WebUserGestureIndicator.cpp',
       'WebUserGestureToken.cpp',
       'WebUserMediaRequest.cpp',
-      'WebViewBenchmarkSupportImpl.cpp',
-      'WebViewBenchmarkSupportImpl.h',
       'WebViewImpl.cpp',
       'WebViewImpl.h',
       'WebWorkerBase.cpp',
       'WebWorkerBase.h',
       'WebWorkerClientImpl.cpp',
       'WebWorkerClientImpl.h',
       'WebWorkerInfo.cpp',
       'WebWorkerRunLoop.cpp',
       'WorkerAllowMainThreadBridgeBase.cpp',
       'WorkerAllowMainThreadBridgeBase.h',
@@ skipping 97 matching lines @@
         {
           'web_unittest_files': [
             'tests/KeyCodeConversionTestGtk.cpp',
             'tests/WebInputEventFactoryTestGtk.cpp',
           ],
         }
       ],
     ],
   },
 }