Replace compile time guard with runtime flag in blink and remove ENABLE_FAST_MOBILE_SCROLLING in gy…

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 34 matching lines @@
       'enable_oilpan%': 0,
       'gc_tracing%': 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_FAST_MOBILE_SCROLLING=1',
           'ENABLE_MEDIA_CAPTURE=1'
         ],
       }, { # OS!="android"
         'feature_defines': [
           'ENABLE_INPUT_MULTIPLE_FIELDS_UI=1',
           'ENABLE_MEDIA_CAPTURE=0',
           'ENABLE_WEB_AUDIO=1'
         ],
       }],
       # Mac OS X uses Accelerate.framework FFT by default instead of FFmpeg.
@@ skipping 27 matching lines @@
         ],
       }],
       ['gc_tracing==1', {
         'feature_defines': [
           'ENABLE_GC_TRACING=1',
         ],
       }],
     ],
   },
 }