For c++, Generate enum classes instead of enum from mojom.

services/files/shared_impl.cc

Index: services/files/shared_impl.cc
diff --git a/services/files/shared_impl.cc b/services/files/shared_impl.cc
index 830eee3b952ec81c9fccb388854032987602c776..78356aa3357bc9b7d8ba5f7d75e21d5e477cd0db 100644
--- a/services/files/shared_impl.cc
+++ b/services/files/shared_impl.cc
@@ -50,7 +50,7 @@ void StatFD(int fd, FileType type, const StatFDCallback& callback) {
   file_info->mtime->nanoseconds = static_cast<int32_t>(buf.st_mtim.tv_nsec);
 #endif
 
-  callback.Run(ERROR_OK, file_info.Pass());
+  callback.Run(Error::OK, file_info.Pass());
 }
 
 void TouchFD(int fd,
@@ -61,13 +61,13 @@ void TouchFD(int fd,
 
   struct timespec times[2];
   Error error = TimespecOrNowToStandardTimespec(atime.get(), &times[0]);
-  if (error != ERROR_OK) {
+  if (error != Error::OK) {
     callback.Run(error);
     return;
   }
 
   error = TimespecOrNowToStandardTimespec(mtime.get(), &times[1]);
-  if (error != ERROR_OK) {
+  if (error != Error::OK) {
     callback.Run(error);
     return;
   }
@@ -77,7 +77,7 @@ void TouchFD(int fd,
     return;
   }
 
-  callback.Run(ERROR_OK);
+  callback.Run(Error::OK);
 }
 
 }  // namespace files