Tweak for formatting constructor initializers.

pkg/analyzer/test/services/data/style_guide_tests.data

 >>> DO use ; instead of {} for empty constructor bodies
 class Point {
   int x, y;
   Point(this.x, this.y) {}
 }
 <<<
 class Point {
   int x, y;
   Point(this.x, this.y);
 }
@@ skipping 164 matching lines @@
         thirdField = "last";
 }
 <<<
 class MyClass {
   var firstField, secondField, thirdField;
   MyClass()
       : firstField = "some value",
         secondField = "another",
         thirdField = "last";
 }
+>>> DO format constructor initialization lists with each field on its own line.
+class MyClass {
+  MyClass(looooooooooooooonA, looooooooooooooonB) : super(looooooooooooooonA, looooooooooooooonB);
+  MyClass(looooooooooooooonA, looooooooooooooonB) : this(looooooooooooooonA, looooooooooooooonB);
+}
+<<<
+class MyClass {
+  MyClass(looooooooooooooonA, looooooooooooooonB)
+      : super(looooooooooooooonA, looooooooooooooonB);
+  MyClass(looooooooooooooonA, looooooooooooooonB)
+      : this(looooooooooooooonA, looooooooooooooonB);
+}
 >>> DO use a space after : in named parameters and named arguments.
 class ListBox {
   bool showScrollbars;
 
   ListBox({this.showScrollbars: false});
 }
 
 main() {
   new ListBox(showScrollbars:true);
   new ListBox(showScrollbars : true);
@@ skipping 22 matching lines @@
   }
 }
 >>> DO use four spaces for method cascades
 var list = new List()
   ..addAll([1, 2, 3])
   ..addAll([4, 5, 6]);
 <<<
 var list = new List()
     ..addAll([1, 2, 3])
     ..addAll([4, 5, 6]);