Revert of Teach Skia to use discardable memory

Source/platform/blink_platform.gypi

 {
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.cpp',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
       'Clock.h',
       'ColorChooser.cpp',
@@ skipping 545 matching lines @@
       'graphics/Canvas2DImageBufferSurface.h',
       'graphics/Canvas2DLayerBridge.cpp',
       'graphics/Canvas2DLayerBridge.h',
       'graphics/Canvas2DLayerManager.cpp',
       'graphics/Canvas2DLayerManager.h',
       'graphics/Color.cpp',
       'graphics/Color.h',
       'graphics/ColorSpace.h',
       'graphics/CrossfadeGeneratedImage.cpp',
       'graphics/CrossfadeGeneratedImage.h',
-      'graphics/DecodingImageGenerator.cpp',
-      'graphics/DecodingImageGenerator.h',
       'graphics/DeferredImageDecoder.cpp',
       'graphics/DeferredImageDecoder.h',
       'graphics/DiscardablePixelRef.cpp',
       'graphics/DiscardablePixelRef.h',
       'graphics/DisplayList.cpp',
       'graphics/DisplayList.h',
       'graphics/DrawLooper.cpp',
       'graphics/DrawLooper.h',
       'graphics/Extensions3D.cpp',
       'graphics/Extensions3D.h',
@@ skipping 310 matching lines @@
       'testing/TreeTestHelpers.h',
       'text/BidiResolverTest.cpp',
       'text/DateTimeFormatTest.cpp',
       'weborigin/DatabaseIdentifierTest.cpp',
       'weborigin/KURLTest.cpp',
       'weborigin/OriginAccessEntryTest.cpp',
       'weborigin/SecurityOriginTest.cpp',
     ],
   },
 }