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 d3ecc5519f6f0e0bbb8adcc0901f055f0fb74771..6c1fcc4f3acd0b2c38b80d34b9ead497ca6979dd 100644
--- a/gpu/command_buffer/service/context_group.h
+++ b/gpu/command_buffer/service/context_group.h
@@ -129,6 +129,10 @@ 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();
   }
@@ -279,6 +283,7 @@ 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_;