Allow canvases to be GPU-accelerated in Workers

third_party/WebKit/Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'ContentDecryptionModuleResult.h',
@@ skipping 721 matching lines @@
       'graphics/filters/SourceAlpha.cpp',
       'graphics/filters/SourceAlpha.h',
       'graphics/filters/SourceGraphic.cpp',
       'graphics/filters/SourceGraphic.h',
       'graphics/filters/SpotLightSource.cpp',
       'graphics/filters/SpotLightSource.h',
       'graphics/gpu/AcceleratedImageBufferSurface.cpp',
       'graphics/gpu/AcceleratedImageBufferSurface.h',
       'graphics/gpu/SharedContextRateLimiter.cpp',
       'graphics/gpu/SharedContextRateLimiter.h',
+      'graphics/gpu/SharedGpuContext.cpp',
+      'graphics/gpu/SharedGpuContext.h',
       'graphics/gpu/DrawingBuffer.cpp',
       'graphics/gpu/DrawingBuffer.h',
       'graphics/gpu/Extensions3DUtil.cpp',
       'graphics/gpu/Extensions3DUtil.h',
       'graphics/gpu/WebGLImageConversion.cpp',
       'graphics/gpu/WebGLImageConversion.h',
       'graphics/paint/ClipDisplayItem.cpp',
       'graphics/paint/ClipDisplayItem.h',
       'graphics/paint/ClipPaintPropertyNode.h',
       'graphics/paint/ClipPathDisplayItem.cpp',
@@ skipping 702 matching lines @@
       ['use_default_render_theme==1',
         {
           'platform_test_files': [
             'scroll/ScrollbarThemeAuraTest.cpp',
           ],
         }
       ],
     ],
   },
 }