rename SkBitmapChecksummer as SkBitmapHasher, and prepare for it to possibly use

gyp/utils.gyp

 {
   'targets': [
     {
       'target_name': 'utils',
       'product_name': 'skia_utils',
       'type': 'static_library',
       'standalone_static_library': 1,
       'dependencies': [
         'cityhash.gyp:cityhash',
       ],
@@ skipping 39 matching lines @@
         '../include/utils/SkParsePath.h',
         '../include/utils/SkPictureUtils.h',
         '../include/utils/SkRandom.h',
         '../include/utils/SkRTConf.h',
         '../include/utils/SkProxyCanvas.h',
         '../include/utils/SkUnitMappers.h',
         '../include/utils/SkWGL.h',
 
         '../src/utils/SkBase64.cpp',
         '../src/utils/SkBase64.h',
-        '../src/utils/SkBitmapChecksummer.cpp',
-        '../src/utils/SkBitmapChecksummer.h',
+        '../src/utils/SkBitmapHasher.cpp',
+        '../src/utils/SkBitmapHasher.h',
         '../src/utils/SkBitmapTransformer.cpp',
         '../src/utils/SkBitmapTransformer.h',
         '../src/utils/SkBitSet.cpp',
         '../src/utils/SkBitSet.h',
         '../src/utils/SkBoundaryPatch.cpp',
         '../src/utils/SkCamera.cpp',
         '../src/utils/SkCityHash.cpp',
         '../src/utils/SkCityHash.h',
         '../src/utils/SkCubicInterval.cpp',
         '../src/utils/SkCullPoints.cpp',
@@ skipping 148 matching lines @@
       },
     },
   ],
 }
 
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