Try to keep constructor calls together. Fix #119.

test/splitting/constructors.unit

 40 columns                              |
 >>> Single initializers can be on one line
 class Foo extends Bar {
   final int b;
   Foo(int a, this.b) : super(a);
 }
 <<<
 class Foo extends Bar {
   final int b;
   Foo(int a, this.b) : super(a);
@@ skipping 13 matching lines @@
 class Foo extends Bar {
   final int b;
   Foo(int a, int b) : super(a), this.b = b == null ? 0 : b;
 }
 <<<
 class Foo extends Bar {
   final int b;
   Foo(int a, int b)
       : super(a),
         this.b = b == null ? 0 : b;
-}
+}
+>>> try to keep constructor call together
+var longIdentifier = new Thing(
+    argument, argument);
+<<<
+var longIdentifier =
+    new Thing(argument, argument);