make OpenCL optional for skpdiff

gyp/common_variables.gypi

 # Copyright 2012 The Android Open Source Project
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   # Get ready for the ugly...
   #
   # - We have to nest our variables dictionaries multiple levels deep, so that
   #   this and other gyp files can rely on previously-set variable values in
@@ skipping 73 matching lines @@
       'skia_stroke_path_rendering%': 0,
       'skia_android_path_rendering%': 0,
       'skia_texture_cache_mb_limit%': 0,
       'skia_angle%': 0,
       'skia_directwrite%': 0,
       'skia_gpu%': 1,
       'skia_osx_sdkroot%': '',
       'skia_profile_enabled%': 0,
       'skia_win_debuggers_path%': '',
       'skia_shared_lib%': 0,
+      'skia_opencl%': 0,
 
       # These variables determine the default optimization level for different
       # compilers.
       'skia_default_vs_optimization_level': 3, # full (/Ox)
       'skia_default_gcc_optimization_level': 3, # -O3
     },
 
     'conditions': [
       [ 'skia_os == "win" and skia_arch_width == 32 or '
         'skia_os in ["linux", "freebsd", "openbsd", "solaris", "android"] or '
@@ skipping 28 matching lines @@
     'skia_texture_cache_mb_limit%': '<(skia_texture_cache_mb_limit)',
     'skia_angle%': '<(skia_angle)',
     'skia_arch_width%': '<(skia_arch_width)',
     'skia_arch_type%': '<(skia_arch_type)',
     'skia_directwrite%': '<(skia_directwrite)',
     'skia_gpu%': '<(skia_gpu)',
     'skia_win_exceptions%': 0,
     'skia_osx_sdkroot%': '<(skia_osx_sdkroot)',
     'skia_profile_enabled%': '<(skia_profile_enabled)',
     'skia_shared_lib%': '<(skia_shared_lib)',
+    'skia_opencl%': '<(skia_opencl)',
     'skia_static_initializers%': '<(skia_static_initializers)',
     'ios_sdk_version%': '6.0',
     'skia_win_debuggers_path%': '<(skia_win_debuggers_path)',
     'skia_asan_build%': 0,
 
     # These are referenced by our .gypi files that list files (e.g. core.gypi)
     #
     'skia_src_path%': '../src',
     'skia_include_path%': '../include',
   },
 }
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