SkThreadPool and co. are not public.

gyp/public_headers.gypi

 # Include this gypi to include all public header files that exist in the
 # include directory.
 #
 # The list is computed by running 'find include -name *.h' in the root dir of
 # the project.
 #
 {
   'variables': {
     'header_filenames': [
       'animator/SkAnimator.h',
@@ skipping 197 matching lines @@
       'svg/SkSVGPaintState.h',
       'svg/SkSVGParser.h',
       'svg/SkSVGTypes.h',
       'utils/SkBoundaryPatch.h',
       'utils/SkCamera.h',
       'utils/SkCubicInterval.h',
       'utils/SkCullPoints.h',
       'utils/SkDebugUtils.h',
       'utils/SkDeferredCanvas.h',
       'utils/SkDumpCanvas.h',
-      'utils/SkDumpCanvas.h',
-      'utils/SkInterpolator.h',
       'utils/SkInterpolator.h',
       'utils/SkLayer.h',
       'utils/SkLua.h',
-      'utils/SkLua.h',
       'utils/SkLuaCanvas.h',
       'utils/SkMatrix44.h',
-      'utils/SkMatrix44.h',
       'utils/SkMeshUtils.h',
       'utils/SkNWayCanvas.h',
       'utils/SkNinePatch.h',
       'utils/SkNullCanvas.h',
       'utils/SkParse.h',
-      'utils/SkParse.h',
-      'utils/SkParsePaint.h',
       'utils/SkParsePaint.h',
       'utils/SkParsePath.h',
       'utils/SkPathUtils.h',
       'utils/SkPictureUtils.h',
       'utils/SkProxyCanvas.h',
       'utils/SkRTConf.h',
-      'utils/SkRTConf.h',
       'utils/SkRandom.h',
-      'utils/SkRunnable.h',
-      'utils/SkRunnable.h',
-      'utils/SkThreadPool.h',
-      'utils/SkThreadPool.h',
-      'utils/SkWGL.h',
       'utils/SkWGL.h',
       'utils/ios/SkStream_NSData.h',
       'utils/mac/SkCGUtils.h',
       'utils/win/SkAutoCoInitialize.h',
       'utils/win/SkHRESULT.h',
       'utils/win/SkIStream.h',
       'utils/win/SkTScopedComPtr.h',
       'views/SkApplication.h',
       'views/SkBGViewArtist.h',
       'views/SkEvent.h',
@@ skipping 25 matching lines @@
       'views/unix/keysym2ucs.h',
       'xml/SkBML_WXMLParser.h',
       'xml/SkBML_XMLParser.h',
       'xml/SkDOM.h',
       'xml/SkJS.h',
       'xml/SkXMLParser.h',
       'xml/SkXMLWriter.h',
     ],
   },
 }