[WIP] support arm_neon_optional flag in blink.

Source/build/features.gypi

 #
 # 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 29 matching lines @@
     # We have to nest variables inside variables so that they can be overridden
     # through GYP_DEFINES.
     'variables': {
       # Enables the Oilpan garbage-collection infrastructure.
       'enable_oilpan%': 0,
       'gc_profile_heap%': 0,
       'gc_profile_marking%': 0,
       'blink_logging_always_on%': 0,
     },
     'conditions': [
+      ['arm_neon == 1', {
+        'feature_defines': [
+          'WTF_CPU_ARM_NEON',
+        ],
+      }],
+      ['arm_neon_optional == 1 and (OS=="linux" or OS=="android")', {
+        'feature_defines': [
+          'WTF_CPU_ARM_NEON_OPTIONAL',
+        ],
+      }],
       ['use_concatenated_impulse_responses==1', {
         # Use concatenated HRTF impulse responses
         'feature_defines': ['WTF_USE_CONCATENATED_IMPULSE_RESPONSES=1'],
       }],
       ['OS!="android"', {
         'feature_defines': [
           'ENABLE_INPUT_MULTIPLE_FIELDS_UI=1',
           'ENABLE_WEB_AUDIO=1'
         ],
       }],
@@ skipping 34 matching lines @@
         ],
       }],
       ['blink_logging_always_on==1', {
         'feature_defines': [
           'LOG_DISABLED=0',
         ],
       }],
     ],
   },
 }