Add a basic Dialog

sky/sdk/lib/widgets/dialog.dart

Index: sky/sdk/lib/widgets/dialog.dart
diff --git a/sky/sdk/lib/widgets/dialog.dart b/sky/sdk/lib/widgets/dialog.dart
new file mode 100644
index 0000000000000000000000000000000000000000..36a171aeb222a81421d997c060e414daaca3e462
--- /dev/null
+++ b/sky/sdk/lib/widgets/dialog.dart
@@ -0,0 +1,53 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'basic.dart';
+import 'material.dart';
+
+class Dialog extends Component {
+  Dialog({
+    String key,
+    this.title,
+    this.content,
+    this.actions,
+    this.onDismiss
+  }) : super(key: key);
+
+  final Widget title;
+  final Widget content;
+  final Widget actions;
+  final Function onDismiss;
+
+  Widget build() {
+    Container mask = new Container(
+      decoration: const BoxDecoration(
+        backgroundColor: const Color(0x7F000000)));
+
+    List<Widget> children = new List<Widget>();
+
+    if (title != null)
+      children.add(title);
+
+    if (content != null)
+      children.add(content);
+
+    if (actions != null)
+      children.add(content);
+
+    return new Stack([
+      new EventListenerNode(mask, onGestureTap: (_) => onDismiss()),
+      new Center(
+        child: new ConstrainedBox(
+          constraints: new BoxConstraints(minWidth: 280.0),
+          child: new Material(
+            level: 4,
+            child: new ShrinkWrapWidth(
+              child: new Block(children)
+            )
+          )
+        )
+      )
+    ]);
+  }
+}