Completely removed the Extensions3D class (Take 2)

Source/platform/blink_platform.gypi

 {
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.cpp',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
       'Clock.h',
       'ColorChooser.cpp',
@@ skipping 569 matching lines @@
       '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',
       'graphics/FrameData.cpp',
       'graphics/FrameData.h',
       'graphics/GeneratedImage.cpp',
       'graphics/GeneratedImage.h',
       'graphics/Gradient.cpp',
       'graphics/Gradient.h',
       'graphics/GradientGeneratedImage.cpp',
       'graphics/GradientGeneratedImage.h',
       'graphics/GraphicsContext.cpp',
       'graphics/GraphicsContext.h',
@@ skipping 322 matching lines @@
       'animation/TimingFunctionTestHelper.cpp',
       'animation/TimingFunctionTestHelper.h',
       'animation/TimingFunctionTestHelperTest.cpp',
       'graphics/DeferredImageDecoderTest.cpp',
       'graphics/ImageDecodingStoreTest.cpp',
       'graphics/ImageFrameGeneratorTest.cpp',
       'graphics/test/MockImageDecoder.h',
     ],
   },
 }