Change mojo enums to be scoped enums in the generated C++ bindings.

device/serial/buffer.cc

Index: device/serial/buffer.cc
diff --git a/device/serial/buffer.cc b/device/serial/buffer.cc
index 2475e0161b258d846d1c10624e5e444f8246013e..c6eeea2607651d69dbfad82dc8640d30dd62a975 100644
--- a/device/serial/buffer.cc
+++ b/device/serial/buffer.cc
@@ -30,7 +30,7 @@ uint32_t SendBuffer::GetSize() {
 }
 
 void SendBuffer::Done(uint32_t bytes_read) {
-  callback_.Run(bytes_read, device::serial::SEND_ERROR_NONE);
+  callback_.Run(bytes_read, device::serial::SendError::NONE);
 }
 
 void SendBuffer::DoneWithError(uint32_t bytes_read, int32_t error) {
@@ -54,7 +54,7 @@ uint32_t ReceiveBuffer::GetSize() {
 }
 
 void ReceiveBuffer::Done(uint32_t bytes_written) {
-  callback_.Run(bytes_written, device::serial::RECEIVE_ERROR_NONE);
+  callback_.Run(bytes_written, device::serial::ReceiveError::NONE);
 }
 
 void ReceiveBuffer::DoneWithError(uint32_t bytes_written, int32_t error) {