SkyDemo.apk should show thumbmails when offline

We now get the thumbnails from the root bundle when offline and otherwise fall
back to the network.

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

Review URL: https://codereview.chromium.org/1212343009.

sdk/example/demo_launcher/lib/main.dart

@@ -5,6 +5,7 @@
 import 'dart:sky';
 
 import 'package:mojom/intents/intents.mojom.dart';
+import 'package:sky/mojo/asset_bundle.dart';
 import 'package:sky/mojo/shell.dart' as shell;
 import 'package:sky/painting/box_painter.dart';
 import 'package:sky/theme/colors.dart' as colors;
@@ -18,6 +19,15 @@ import 'package:sky/widgets/scaffold.dart';
 import 'package:sky/widgets/theme.dart';
 import 'package:sky/widgets/tool_bar.dart';
 
+AssetBundle _initBundle() {
+  if (rootBundle != null)
+    return rootBundle;
+  const String _kAssetBase = '..';
+  return new NetworkAssetBundle(Uri.base.resolve(_kAssetBase));
+}
+
+final AssetBundle _bundle = _initBundle();
+
 void launch(String relativeUrl, String bundle) {
   Uri url = Uri.base.resolve(relativeUrl);
 
@@ -60,7 +70,7 @@ List<Widget> demos = [
     textTheme: typography.black,
     decoration: new BoxDecoration(
       backgroundImage: new BackgroundImage(
-        src: '../assets/stocks_thumbnail.png',
+        image: _bundle.loadImage('assets/stocks_thumbnail.png'),
         fit: BackgroundFit.cover
       )
     )
@@ -72,7 +82,7 @@ List<Widget> demos = [
     textTheme: typography.white,
     decoration: new BoxDecoration(
       backgroundImage: new BackgroundImage(
-        src: '../assets/game_thumbnail.png',
+        image: _bundle.loadImage('assets/game_thumbnail.png'),
         fit: BackgroundFit.cover
       )
     )
@@ -96,7 +106,7 @@ List<Widget> demos = [
     decoration: new BoxDecoration(
       backgroundColor: colors.Black,
       backgroundImage: new BackgroundImage(
-        src: '../assets/sector_thumbnail.png',
+        image: _bundle.loadImage('assets/sector_thumbnail.png'),
         fit: BackgroundFit.cover
       )
     )

sdk/lib/painting/box_painter.dart

@@ -2,13 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 import 'dart:sky' show Point, Offset, Size, Rect, Color, Paint, Path;
 
 import '../base/lerp.dart';
 import 'shadows.dart';
-import 'package:sky/mojo/net/image_cache.dart' as image_cache;
 
 class BorderSide {
   const BorderSide({
@@ -140,19 +140,18 @@ enum BackgroundRepeat { repeat, repeatX, repeatY, noRepeat }
 // to do animated images.
 
 class BackgroundImage {
-  final String src;
   final BackgroundFit fit;
   final BackgroundRepeat repeat;
   BackgroundImage({
-    this.src,
+    Future<sky.Image> image,
     this.fit: BackgroundFit.scaleDown,
     this.repeat: BackgroundRepeat.noRepeat
   }) {
-    image_cache.load(src).then((image) {
-      if (image == null)
+    image.then((resolvedImage) {
+      if (resolvedImage == null)
         return;
-      _image = image;
-      _size = new Size(image.width.toDouble(), image.height.toDouble());
+      _image = resolvedImage;
+      _size = new Size(resolvedImage.width.toDouble(), resolvedImage.height.toDouble());
       for (Function listener in _listeners) {
         listener();
       }
@@ -174,7 +173,7 @@ class BackgroundImage {
     _listeners.remove(listener);
   }
 
-  String toString() => 'BackgroundImage($src, $fit, $repeat)';
+  String toString() => 'BackgroundImage($fit, $repeat)';
 }
 
 enum Shape { rectangle, circle }