Add GL_CHROMIUM_screen_space_antialiasing to support alternative AA

gpu/command_buffer/service/feature_info.cc

Index: gpu/command_buffer/service/feature_info.cc
diff --git a/gpu/command_buffer/service/feature_info.cc b/gpu/command_buffer/service/feature_info.cc
index b3c5be635f8d86666d862165c9912a4e70f08ff6..1505e8c9fd5dc535c42c5f07d4c974b104a89d50 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -130,6 +130,7 @@ FeatureInfo::FeatureFlags::FeatureFlags()
       use_core_framebuffer_multisample(false),
       multisampled_render_to_texture(false),
       use_img_for_multisampled_render_to_texture(false),
+      chromium_screen_space_antialiasing(false),
       oes_standard_derivatives(false),
       oes_egl_image_external(false),
       oes_depth24(false),
@@ -733,6 +734,11 @@ void FeatureInfo::InitializeFeatures() {
     }
   }
 
+  if (extensions.Contains("GL_INTEL_framebuffer_CMAA")) {
+    feature_flags_.chromium_screen_space_antialiasing = true;
+    AddExtensionString("GL_CHROMIUM_screen_space_antialiasing");
+  }
+
   if (extensions.Contains("GL_OES_depth24") || gfx::HasDesktopGLFeatures() ||
       gl_version_info_->is_es3) {
     AddExtensionString("GL_OES_depth24");