Add GL_CHROMIUM_screen_space_antialiasing to support alternative AA

gpu/command_buffer/service/feature_info.h

Index: gpu/command_buffer/service/feature_info.h
diff --git a/gpu/command_buffer/service/feature_info.h b/gpu/command_buffer/service/feature_info.h
index dae148af2a6e29d1ec629a997a35204efaada621..9bd0f935dab87f0fda5c24b071904db52c121a62 100644
--- a/gpu/command_buffer/service/feature_info.h
+++ b/gpu/command_buffer/service/feature_info.h
@@ -42,6 +42,7 @@ class GPU_EXPORT FeatureInfo : public base::RefCounted<FeatureInfo> {
     bool multisampled_render_to_texture;
     // Use the IMG GLenum values and functions rather than EXT.
     bool use_img_for_multisampled_render_to_texture;
+    bool chromium_screen_space_antialiasing;
     bool oes_standard_derivatives;
     bool oes_egl_image_external;
     bool oes_depth24;