command_buffer: Implement CHROMIUM_framebuffer_mixed_samples extension

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 76494a6c8b24f168cf6cd084ba470bf900a8b668..d179e40bc461748923b2d0a1fd1012db7e9043e7 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -168,6 +168,7 @@ FeatureInfo::FeatureFlags::FeatureFlags()
       angle_texture_usage(false),
       ext_texture_storage(false),
       chromium_path_rendering(false),
+      chromium_framebuffer_mixed_samples(false),
       blend_equation_advanced(false),
       blend_equation_advanced_coherent(false),
       ext_texture_rg(false),
@@ -1168,6 +1169,14 @@ void FeatureInfo::InitializeFeatures() {
     }
   }
 
+  if (enable_gl_path_rendering_switch_ &&
+      !workarounds_.disable_gl_path_rendering &&
+      extensions.Contains("GL_NV_framebuffer_mixed_samples")) {
+    AddExtensionString("GL_CHROMIUM_framebuffer_mixed_samples");
+    feature_flags_.chromium_framebuffer_mixed_samples = true;
+    validators_.g_l_state.AddValue(GL_COVERAGE_MODULATION_CHROMIUM);
+  }
+
   if ((gl_version_info_->is_es3 || gl_version_info_->is_desktop_core_profile ||
        extensions.Contains("GL_EXT_texture_rg") ||
        extensions.Contains("GL_ARB_texture_rg")) &&