Fixes for empty class and method bodies.

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 146 matching lines @@
 <<<
 spaces() {
   var numbers = <int>[1, 2, (3 + 4)];
 }
 >>> DO use a space before { in function and method bodies.
 getEmptyFn(a){
   return (){};
 }
 <<<
 getEmptyFn(a) {
-  return () {
-  };
+  return () {};
 }
 >>> DO format constructor initialization lists with each field on its own line.
 class MyClass {
   var firstField, secondField, thirdField;
   MyClass() : firstField = "some value", secondField = "another",
         thirdField = "last";
 }
 <<<
 class MyClass {
   var firstField, secondField, thirdField;
@@ skipping 37 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]);