Reland: Added SyncToken command buffer trait to help with IPC messages

gpu/ipc/gpu_command_buffer_traits.h

Index: gpu/ipc/gpu_command_buffer_traits.h
diff --git a/gpu/ipc/gpu_command_buffer_traits.h b/gpu/ipc/gpu_command_buffer_traits.h
index d99d4654bffa59170a8da29965c8db2a1055e92f..b726f7eac077d97da1a8b6fa60db2f186cb4ec79 100644
--- a/gpu/ipc/gpu_command_buffer_traits.h
+++ b/gpu/ipc/gpu_command_buffer_traits.h
@@ -13,6 +13,7 @@
 namespace gpu {
 struct Mailbox;
 struct MailboxHolder;
+struct SyncToken;
 union ValueState;
 }
 
@@ -26,6 +27,14 @@ struct GPU_EXPORT ParamTraits<gpu::CommandBuffer::State> {
   static void Log(const param_type& p, std::string* l);
 };
 
+template <>
+struct GPU_EXPORT ParamTraits<gpu::SyncToken> {
+  typedef gpu::SyncToken param_type;
+  static void Write(Message* m, const param_type& p);
+  static bool Read(const Message* m, base::PickleIterator* iter, param_type* p);
+  static void Log(const param_type& p, std::string* l);
+};
+
 template<>
 struct GPU_EXPORT ParamTraits<gpu::Mailbox> {
   typedef gpu::Mailbox param_type;