Revert of SkThreadPool ~~> SkTaskGroup

gyp/utils.gypi

 # Include this gypi to include all 'utils' files
 # The parent gyp/gypi file must define
 #       'skia_src_path'     e.g. skia/trunk/src
 #       'skia_include_path' e.g. skia/trunk/include
 #
 # The skia build defines these in common_variables.gypi
 #
 {
     'sources': [
         # Classes for a threadpool.
         '<(skia_src_path)/utils/SkCondVar.h',
         '<(skia_src_path)/utils/SkRunnable.h',
+        '<(skia_src_path)/utils/SkThreadPool.h',
         '<(skia_src_path)/utils/SkCondVar.cpp',
 
         '<(skia_include_path)/utils/SkBoundaryPatch.h',
         '<(skia_include_path)/utils/SkFrontBufferedStream.h',
         '<(skia_include_path)/utils/SkCamera.h',
         '<(skia_include_path)/utils/SkCanvasStateUtils.h',
         '<(skia_include_path)/utils/SkCubicInterval.h',
         '<(skia_include_path)/utils/SkCullPoints.h',
         '<(skia_include_path)/utils/SkDebugUtils.h',
         '<(skia_include_path)/utils/SkDeferredCanvas.h',
@@ skipping 103 matching lines @@
         '<(skia_src_path)/utils/win/SkIStream.cpp',
         '<(skia_src_path)/utils/win/SkWGL_win.cpp',
 
         #testing
         '<(skia_src_path)/fonts/SkGScalerContext.cpp',
         '<(skia_src_path)/fonts/SkGScalerContext.h',
         '<(skia_src_path)/fonts/SkTestScalerContext.cpp',
         '<(skia_src_path)/fonts/SkTestScalerContext.h',
     ],
 }