Format enums. Fix #120.

lib/src/source_visitor.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart_style.src.source_visitor;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/source.dart';
 
@@ skipping 505 matching lines @@
 
   visitEmptyFunctionBody(EmptyFunctionBody node) {
     token(node.semicolon);
   }
 
   visitEmptyStatement(EmptyStatement node) {
     token(node.semicolon);
   }
 
   visitEnumConstantDeclaration(EnumConstantDeclaration node) {
-    throw new UnimplementedError("Enum formatting is not implemented yet.");
+    visit(node.name);
   }
 
   visitEnumDeclaration(EnumDeclaration node) {
-    throw new UnimplementedError("Enum formatting is not implemented yet.");
+    visitDeclarationMetadata(node.metadata);
+
+    token(node.keyword);
+    space();
+    visit(node.name);
+    space();
+    token(node.leftBracket);
+
+    _writer.indent();
+    _writer.startMultisplit();
+    _writer.multisplit(space: true);
+
+    visitCommaSeparatedNodes(node.constants, between: () {
+      _writer.multisplit(space: true);
+    });
+
+    // Trailing comma.
+    if (node.rightBracket.previous.lexeme == ",") {
+      token(node.rightBracket.previous);
+    }
+
+    _writer.unindent();
+    _writer.multisplit(space: true);
+    token(node.rightBracket);
   }
 
   visitExportDirective(ExportDirective node) {
     visitDeclarationMetadata(node.metadata);
 
     _simpleStatement(node, () {
       token(node.keyword);
       space();
       visit(node.uri);
       _visitCombinators(node.combinators);
@@ skipping 1234 matching lines @@
   /// Gets the 1-based line number that the beginning of [token] lies on.
   int _startLine(Token token) => _lineInfo.getLocation(token.offset).lineNumber;
 
   /// Gets the 1-based line number that the end of [token] lies on.
   int _endLine(Token token) => _lineInfo.getLocation(token.end).lineNumber;
 
   /// Gets the 1-based column number that the beginning of [token] lies on.
   int _startColumn(Token token) =>
       _lineInfo.getLocation(token.offset).columnNumber;
 }