Reland #1: Fix the mechanism by which Blink determines OSX version number.

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 962 matching lines @@
       'graphics/RecordingImageBufferSurfaceTest.cpp',
       'graphics/ThreadSafeDataTransportTest.cpp',
       'graphics/filters/FilterOperationsTest.cpp',
       'graphics/filters/ImageFilterBuilderTest.cpp',
       'graphics/gpu/DrawingBufferTest.cpp',
       'graphics/paint/DisplayItemPropertyTreeBuilderTest.cpp',
       'graphics/paint/DisplayItemListTest.cpp',
       'graphics/paint/DisplayItemTest.cpp',
       'image-decoders/FastSharedBufferReaderTest.cpp',
       'image-decoders/ImageDecoderTest.cpp',
+      'mac/VersionUtilMacTest.mm',
       'network/FormDataTest.cpp',
       'network/HTTPParsersTest.cpp',
       'network/ResourceRequestTest.cpp',
       'scheduler/CancellableTaskFactoryTest.cpp',
       'scroll/ScrollableAreaTest.cpp',
       'testing/ArenaTestHelpers.h',
       'testing/TreeTestHelpers.cpp',
       'testing/TreeTestHelpers.h',
       'text/BidiResolverTest.cpp',
       'text/DateTimeFormatTest.cpp',
@@ skipping 55 matching lines @@
       ['os_posix==1 and OS!="mac"',
         {
           'platform_test_files': [
             'text/LocaleICUTest.cpp',
           ],
         }
       ],
     ],
   },
 }