pub exit codes should be const

sdk/lib/_internal/pub/lib/src/exit_codes.dart

Index: sdk/lib/_internal/pub/lib/src/exit_codes.dart
diff --git a/sdk/lib/_internal/pub/lib/src/exit_codes.dart b/sdk/lib/_internal/pub/lib/src/exit_codes.dart
index 028fd1c97b63f40418dbbd95dbb571c6a183a1f0..156e49e4e432439125dfc2d8021746b04f3b8fd0 100644
--- a/sdk/lib/_internal/pub/lib/src/exit_codes.dart
+++ b/sdk/lib/_internal/pub/lib/src/exit_codes.dart
@@ -10,46 +10,46 @@
 library pub.exit_codes;
 
 /// The command was used incorrectly.
-final USAGE = 64;
+const USAGE = 64;
 
 /// The input data was incorrect.
-final DATA = 65;
+const DATA = 65;
 
 /// An input file did not exist or was unreadable.
-final NO_INPUT = 66;
+const NO_INPUT = 66;
 
 /// The user specified did not exist.
-final NO_USER = 67;
+const NO_USER = 67;
 
 /// The host specified did not exist.
-final NO_HOST = 68;
+const NO_HOST = 68;
 
 /// A service is unavailable.
-final UNAVAILABLE = 69;
+const UNAVAILABLE = 69;
 
 /// An internal software error has been detected.
-final SOFTWARE = 70;
+const SOFTWARE = 70;
 
 /// An operating system error has been detected.
-final OS = 71;
+const OS = 71;
 
 /// Some system file did not exist or was unreadable.
-final OS_FILE = 72;
+const OS_FILE = 72;
 
 /// A user-specified output file cannot be created.
-final CANT_CREATE = 73;
+const CANT_CREATE = 73;
 
 /// An error occurred while doing I/O on some file.
-final IO = 74;
+const IO = 74;
 
 /// Temporary failure, indicating something that is not really an error.
-final TEMP_FAIL = 75;
+const TEMP_FAIL = 75;
 
 /// The remote system returned something invalid during a protocol exchange.
-final PROTOCOL = 76;
+const PROTOCOL = 76;
 
 /// The user did not have sufficient permissions.
-final NO_PERM = 77;
+const NO_PERM = 77;
 
 /// Something was unconfigured or mis-configured.
-final CONFIG = 78;
+const CONFIG = 78;