DM: make GPU tasks multithreaded again. Big refactor.

gyp/utils.gyp

 # Gyp for utils.
 {
   'targets': [
     {
       'target_name': 'utils',
       'product_name': 'skia_utils',
       'type': 'static_library',
       'standalone_static_library': 1,
       'dependencies': [
         'core.gyp:*',
@@ skipping 12 matching lines @@
         '../src/utils',
       ],
       'sources': [
         # Classes for a threadpool.
         '../include/utils/SkCondVar.h',
         '../include/utils/SkCountdown.h',
         '../include/utils/SkRunnable.h',
         '../include/utils/SkThreadPool.h',
         '../src/utils/SkCondVar.cpp',
         '../src/utils/SkCountdown.cpp',
-        '../src/utils/SkThreadPool.cpp',
 
         '../include/utils/SkBoundaryPatch.h',
         '../include/utils/SkFrontBufferedStream.h',
         '../include/utils/SkCamera.h',
         '../include/utils/SkCanvasStateUtils.h',
         '../include/utils/SkCubicInterval.h',
         '../include/utils/SkCullPoints.h',
         '../include/utils/SkDebugUtils.h',
         '../include/utils/SkDeferredCanvas.h',
         '../include/utils/SkDumpCanvas.h',
@@ skipping 176 matching lines @@
         }],
         ['skia_run_pdfviewer_in_gm', {
           'defines': [
             'SK_BUILD_NATIVE_PDF_RENDERER',
           ],
         }],
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '../include/utils',
+          '../src/utils',
         ],
       },
     },
   ],
 }