Add SkCanvasStack and update the Canvas utilities to use it.

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 48 matching lines @@
         '../include/utils/SkWGL.h',
 
         '../src/utils/SkBase64.cpp',
         '../src/utils/SkBase64.h',
         '../src/utils/SkBitmapHasher.cpp',
         '../src/utils/SkBitmapHasher.h',
         '../src/utils/SkBitSet.cpp',
         '../src/utils/SkBitSet.h',
         '../src/utils/SkBoundaryPatch.cpp',
         '../src/utils/SkCamera.cpp',
+        '../src/utils/SkCanvasStack.h',
+        '../src/utils/SkCanvasStack.cpp',
         '../src/utils/SkCanvasStateUtils.cpp',
         '../src/utils/SkCubicInterval.cpp',
         '../src/utils/SkCullPoints.cpp',
         '../src/utils/SkDeferredCanvas.cpp',
         '../src/utils/SkDumpCanvas.cpp',
         '../src/utils/SkFloatUtils.h',
         '../src/utils/SkInterpolator.cpp',
         '../src/utils/SkLayer.cpp',
         '../src/utils/SkMatrix44.cpp',
         '../src/utils/SkMD5.cpp',
@@ skipping 139 matching lines @@
       },
     },
   ],
 }
 
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 # tab-width:2
 # indent-tabs-mode:nil
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