Formatting constructor initializers a la the Style Guide.

pkg/analyzer_experimental/test/services/formatter_test.dart

Index: pkg/analyzer_experimental/test/services/formatter_test.dart
===================================================================
--- pkg/analyzer_experimental/test/services/formatter_test.dart	(revision 28103)
+++ pkg/analyzer_experimental/test/services/formatter_test.dart	(working copy)
@@ -598,7 +598,8 @@
           '}\n',
           'class A {\n'
           '  int _a;\n'
-          '  A(a) : _a = a;\n'
+          '  A(a)\n'
+          '      : _a = a;\n'
           '}\n'
         );
     });
@@ -622,6 +623,20 @@
         'part of foo;\n'
       );
     });
+    
+    test('CU (cons inits)', () {
+      expectCUFormatsTo('class X {\n'
+          '  var x, y;\n'
+          '  X() : x = 1, y = 2;\n'
+          '}\n', 
+          'class X {\n'
+          '  var x, y;\n'
+          '  X()\n'
+          '      : x = 1,\n' 
+          '        y = 2;\n'
+          '}\n'
+      );
+    });
 
     test('stmt', () {
       expectStmtFormatsTo(