Allow assertions to be enabled in Blink Release builds.

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 25 matching lines @@
       'ENABLE_SVG_FONTS=1',
       # WTF_USE_DYNAMIC_ANNOTATIONS=1 may be defined in build/common.gypi
       # We can't define it here because it should be present only
       # in Debug or release_valgrind_build=1 builds.
     ],
     # 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_tracing%': 0
+      'gc_tracing%': 0,
+      'blink_asserts_always_on%': 0,
     },
     'conditions': [
       ['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 27 matching lines @@
       ['enable_oilpan==1', {
         'feature_defines': [
           'ENABLE_OILPAN=1',
         ],
       }],
       ['gc_tracing==1', {
         'feature_defines': [
           'ENABLE_GC_TRACING=1',
         ],
       }],
+      ['blink_asserts_always_on==1', {
+        'feature_defines': [
+          'ENABLE_ASSERT=1',
+        ],
+      }],
     ],
   },
 }