Add compile flag to force usage of distance fields for all SkPaints.

gyp/common_conditions.gypi

 # conditions used in both common.gypi and skia.gyp in chromium
 #
 {
   'defines': [
     'SK_ALLOW_STATIC_GLOBAL_INITIALIZERS=<(skia_static_initializers)',
     'SK_SUPPORT_GPU=<(skia_gpu)',
     'SK_SUPPORT_OPENCL=<(skia_opencl)',
+    'SK_FORCE_DISTANCEFIELD_FONTS=<(skia_force_distancefield_fonts)',
   ],
   'conditions' : [
     [ 'skia_os == "win"',
       {
         'defines': [
           'SK_BUILD_FOR_WIN32',
           '_CRT_SECURE_NO_WARNINGS',
           'GR_GL_FUNCTION_TYPE=__stdcall',
         ],
         'msvs_cygwin_shell': 0,
@@ skipping 511 matching lines @@
       'defines': [
         'SK_USE_POSIX_THREADS',
       ],
     }],
   ], # end 'conditions'
   # The Xcode SYMROOT must be at the root. See build/common.gypi in chromium for more details
   'xcode_settings': {
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }