Renamed Ident to Identifier, added some helper methods and refactored two methods.

--
MOS_MIGRATED_REVID=98922811
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/UserDefinedFunction.java b/src/main/java/com/google/devtools/build/lib/syntax/UserDefinedFunction.java
index 5bb9019..4a5968c 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/UserDefinedFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/UserDefinedFunction.java
@@ -25,7 +25,7 @@
   private final ImmutableList<Statement> statements;
   private final SkylarkEnvironment definitionEnv;
 
-  protected UserDefinedFunction(Ident function,
+  protected UserDefinedFunction(Identifier function,
       FunctionSignature.WithValues<Object, SkylarkType> signature,
       ImmutableList<Statement> statements, SkylarkEnvironment definitionEnv) {
     super(function.getName(), signature, function.getLocation());