Fix "unreachable code" warnings (MSVC warning 4702) in Blink.

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 318 matching lines @@
       ],
       'conditions': [
         ['OS=="win" and component=="shared_library"', {
           'defines': [
             'USING_V8_SHARED',
           ],
         }],
         ['OS=="win"', {
           # In generated bindings code: 'switch contains default but no case'.
           # Disable c4267 warnings until we fix size_t to int truncations.
-          'msvs_disabled_warnings': [ 4065, 4267 ],
+          # 4702 is disabled because of issues in Bison-generated
+          # XPathGrammar.cpp and CSSGrammar.cpp.
+          'msvs_disabled_warnings': [ 4065, 4267, 4702 ],
         }],
         ['OS in ("linux", "android") and "WTF_USE_WEBAUDIO_IPP=1" in feature_defines', {
           'cflags': [
             '<!@(pkg-config --cflags-only-I ipp)',
           ],
         }],
       ],
     },
     {
       # We'll soon split libwebcore in multiple smaller libraries.
@@ skipping 475 matching lines @@
         '<(SHARED_INTERMEDIATE_DIR)/blink/bindings/V8LayerRect.h',
         '<(SHARED_INTERMEDIATE_DIR)/blink/bindings/V8LayerRectList.cpp',
         '<(SHARED_INTERMEDIATE_DIR)/blink/bindings/V8LayerRectList.h',
       ],
       'sources/': [
         ['exclude', 'testing/js'],
       ],
     },
   ],  # targets
 }