Add clip effect for circles

gyp/gpu.gypi

 # Include this gypi to include all 'gpu' files
 # The parent gyp/gypi file must define
 #       'skia_src_path'     e.g. skia/trunk/src
 #       'skia_include_path' e.g. skia/trunk/include
 #
 # The skia build defines these in common_variables.gypi
 #
 {
   'variables': {
     'skgpu_sources': [
@@ skipping 131 matching lines @@
       '<(skia_src_path)/gpu/effects/GrConvolutionEffect.cpp',
       '<(skia_src_path)/gpu/effects/GrConvolutionEffect.h',
       '<(skia_src_path)/gpu/effects/GrConvexPolyEffect.cpp',
       '<(skia_src_path)/gpu/effects/GrConvexPolyEffect.h',
       '<(skia_src_path)/gpu/effects/GrBicubicEffect.cpp',
       '<(skia_src_path)/gpu/effects/GrBicubicEffect.h',
       '<(skia_src_path)/gpu/effects/GrCustomCoordsTextureEffect.cpp',
       '<(skia_src_path)/gpu/effects/GrCustomCoordsTextureEffect.h',
       '<(skia_src_path)/gpu/effects/GrDistanceFieldTextureEffect.cpp',
       '<(skia_src_path)/gpu/effects/GrDistanceFieldTextureEffect.h',
+      '<(skia_src_path)/gpu/effects/GrOvalEffect.cpp',
+      '<(skia_src_path)/gpu/effects/GrOvalEffect.h',
       '<(skia_src_path)/gpu/effects/GrRRectEffect.cpp',
       '<(skia_src_path)/gpu/effects/GrRRectEffect.h',
       '<(skia_src_path)/gpu/effects/GrSimpleTextureEffect.cpp',
       '<(skia_src_path)/gpu/effects/GrSimpleTextureEffect.h',
       '<(skia_src_path)/gpu/effects/GrSingleTextureEffect.cpp',
       '<(skia_src_path)/gpu/effects/GrSingleTextureEffect.h',
       '<(skia_src_path)/gpu/effects/GrTextureDomain.cpp',
       '<(skia_src_path)/gpu/effects/GrTextureDomain.h',
       '<(skia_src_path)/gpu/effects/GrTextureStripAtlas.cpp',
       '<(skia_src_path)/gpu/effects/GrTextureStripAtlas.h',
@@ skipping 126 matching lines @@
     ],
     'skgpu_null_gl_sources': [
       '<(skia_src_path)/gpu/gl/GrGLCreateNullInterface.cpp',
 
       # Sk files
       '<(skia_include_path)/gpu/gl/SkNullGLContext.h',
       '<(skia_src_path)/gpu/gl/SkNullGLContext.cpp',
     ],
   },
 }