Add gen/third_party/WebKit to include dirs

brightray/brightray.gyp

@@ -35,6 +35,7 @@
           '<(libchromiumcontent_src_dir)/third_party/khronos',
           '<(libchromiumcontent_src_dir)/third_party/WebKit',
           '<(libchromiumcontent_dir)/gen',
+          '<(libchromiumcontent_dir)/gen/third_party/WebKit',
         ],
       },
       'sources': [ '<@(brightray_sources)' ],