Add a basic Dialog

The dialog will need many more features to be complete, but this class is a
basic skeleton of what we'll need.

R=jackson@google.com, jackson@chromium.org

Review URL: https://codereview.chromium.org/1189893002.

sdk/BUILD.gn

@@ -103,6 +103,7 @@ dart_pkg("sdk") {
     "lib/widgets/basic.dart",
     "lib/widgets/button_base.dart",
     "lib/widgets/checkbox.dart",
+    "lib/widgets/dialog.dart",
     "lib/widgets/drawer.dart",
     "lib/widgets/drawer_header.dart",
     "lib/widgets/fixed_height_scrollable.dart",

sdk/lib/widgets/dialog.dart

+// 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)
+            )
+          )
+        )
+      )
+    ]);
+  }
+}

tests/widgets/dialog-expected.txt

+CONSOLE: TestRenderView enabled
+CONSOLE: 
+PAINT FOR FRAME #1 ----------------------------------------------
+1 | TestDisplayList() constructor: 800.0 x 600.0
+------------------------------------------------------------------------
+CONSOLE: 
+PAINT FOR FRAME #2 ----------------------------------------------
+2 | TestDisplayList() constructor: 800.0 x 600.0
+2 | paintChild RenderStack at Point(0.0, 0.0)
+2 |  | TestDisplayList() constructor: 800.0 x 600.0
+2 |  | paintChild RenderDecoratedBox at Point(0.0, 0.0)
+2 |  |  | TestDisplayList() constructor: 800.0 x 600.0
+2 |  |  | drawRect(Rect.fromLTRB(0.0, 0.0, 800.0, 600.0), Paint(Color(0x7f000000)))
+2 |  | paintChild RenderPositionedBox at Point(0.0, 0.0)
+2 |  |  | TestDisplayList() constructor: 800.0 x 600.0
+2 |  |  | paintChild RenderConstrainedBox at Point(260.0, 284.0)
+2 |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+2 |  |  |  | drawRRect(Instance of 'RRect', Paint(Color(0xfffafafa)))
+2 |  |  |  | paintChild RenderParagraph at Point(0.0, 0.0)
+2 |  |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+2 |  |  |  | paintChild RenderParagraph at Point(0.0, 16.0)
+2 |  |  |  |  | TestDisplayList() constructor: 800.0 x 600.0
+------------------------------------------------------------------------
+PAINTED 2 FRAMES

tests/widgets/dialog.dart

+// 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 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/dialog.dart';
+
+import '../resources/display_list.dart';
+
+main() async {
+  WidgetTester tester = new WidgetTester();
+
+  await tester.test(() {
+    return new Dialog(
+      title: new Text("I am a title"),
+      content: new Text("I am some content")
+    );
+  });
+
+  await tester.endTest();
+}