Roll Observatory packages and add a roll script

packages/dart_style/test/regression/0200/0237.unit

+>>>
+class Bar {
+  void foo() {
+    blah.method(someLongArgument, andAnotherOne, andAThirdOne, andOneMore)
+      .then((var x) {
+        var y = x * 2;
+      });
+  }
+}
+<<<
+class Bar {
+  void foo() {
+    blah
+        .method(someLongArgument, andAnotherOne, andAThirdOne, andOneMore)
+        .then((var x) {
+      var y = x * 2;
+    });
+  }
+}