command_buffer: Implement EXT_blend_func_extended

gpu/command_buffer/service/context_group.h

Index: gpu/command_buffer/service/context_group.h
diff --git a/gpu/command_buffer/service/context_group.h b/gpu/command_buffer/service/context_group.h
index ad2c5df0b19b3873d134a230008c31f5acd4fbf5..fa9d3ac54eb97c723f0d433aa0c838e66c4ce6aa 100644
--- a/gpu/command_buffer/service/context_group.h
+++ b/gpu/command_buffer/service/context_group.h
@@ -123,6 +123,10 @@ class GPU_EXPORT ContextGroup : public base::RefCounted<ContextGroup> {
     return max_draw_buffers_;
   }
 
+  uint32 max_dual_source_draw_buffers() const {
+    return max_dual_source_draw_buffers_;
+  }
+
   FeatureInfo* feature_info() {
     return feature_info_.get();
   }
@@ -271,6 +275,7 @@ class GPU_EXPORT ContextGroup : public base::RefCounted<ContextGroup> {
   uint32 max_vertex_uniform_vectors_;
   uint32 max_color_attachments_;
   uint32 max_draw_buffers_;
+  uint32 max_dual_source_draw_buffers_;
 
   ProgramCache* program_cache_;