Roll Observatory packages and add a roll script

packages/dart_style/web/main.dart

+import 'dart:html';
+
+import 'package:dart_style/dart_style.dart';
+
+TextAreaElement before;
+TextAreaElement after;
+
+int width = 80;
+
+PreElement columnMarker = querySelector(".column-marker");
+InputElement widthInput = querySelector("#width");
+OutputElement widthOutput = querySelector("#width-output");
+
+void main() {
+  before = querySelector("#before") as TextAreaElement;
+  after = querySelector("#after") as TextAreaElement;
+
+  before.onKeyUp.listen((event) {
+    reformat();
+
+    window.localStorage["code"] = before.value;
+  });
+
+  var code = window.localStorage["code"];
+  if (code != null) before.text = code;
+
+  if (window.localStorage.containsKey("width")) {
+    setWidth(window.localStorage["width"]);
+  }
+
+  widthInput.onInput.listen((event) {
+    setWidth(widthInput.value);
+    window.localStorage["width"] = widthInput.value;
+  });
+
+  reformat();
+}
+
+void reformat() {
+  var source = before.value;
+
+  try {
+    after.value = new DartFormatter(pageWidth: width).format(source);
+    return;
+  } on FormatterException {
+    // Do nothing.
+  }
+
+  // Maybe it's a statement.
+  try {
+    after.value = new DartFormatter(pageWidth: width).formatStatement(source);
+  } on FormatterException catch (err) {
+    after.value = "Format failed:\n$err";
+  }
+}
+
+void setWidth(String widthString) {
+  width = int.parse(widthString);
+
+  widthInput.value = widthString;
+  widthOutput.value = widthString;
+
+  var pad = " " * width + "|";
+  columnMarker.innerHtml = "$pad $width columns" + "\n$pad" * 29;
+  reformat();
+}