gpu: Add out-of-line copy ctors for complex classes.

gpu/command_buffer/service/vertex_attrib_manager.cc

Index: gpu/command_buffer/service/vertex_attrib_manager.cc
diff --git a/gpu/command_buffer/service/vertex_attrib_manager.cc b/gpu/command_buffer/service/vertex_attrib_manager.cc
index 5d87aea211d30b68feca861b2831f1ec8ecd9764..fc3941083b102d3bec12001d05518afeb09d479f 100644
--- a/gpu/command_buffer/service/vertex_attrib_manager.cc
+++ b/gpu/command_buffer/service/vertex_attrib_manager.cc
@@ -41,6 +41,8 @@ VertexAttrib::VertexAttrib()
       list_(NULL) {
 }
 
+VertexAttrib::VertexAttrib(const VertexAttrib& other) = default;
+
 VertexAttrib::~VertexAttrib() {
 }