Revert harder, removing SkTaskGroup.cpp from core temporarily.

gyp/pathops_skpclip.gyp

 # GYP file to build pathops skp clip test.
 {
   'includes': [
     'apptype_console.gypi',
   ],
   'targets': [
     {
       'target_name': 'pathops_skpclip',
       'type': 'executable',
       'include_dirs': [
         '../src/core',
         '../src/effects',
         '../src/lazy',
         '../src/pathops',
         '../src/pipe/utils',
         '../src/utils',
       ],
       'dependencies': [
         'flags.gyp:flags',
         'skia_lib.gyp:skia_lib',
         'tools.gyp:crash_handler',
         'tools.gyp:resources',
       ],
       'sources': [
+        '../src/core/SkTaskGroup.cpp',
                 '../tests/PathOpsDebug.cpp',
         '../tests/PathOpsSkpClipTest.cpp',
       ],
       'conditions': [
         [ 'skia_android_framework == 1', {
           'libraries': [
             '-lskia',
           ],
           'libraries!': [
             '-lz',
             '-llog',
           ],
         }],
         [ 'skia_gpu == 1', {
           'include_dirs': [
             '../src/gpu',
           ],
         }],
       ],
     },
   ],
 }