Move image loading out of C++ into Dart

sky/sdk/README.md

 Contributing
 ============
 
 [sky_sdk](https://github.com/domokit/sky_sdk) is generated from the
 [mojo repository](https://github.com/domokit/mojo) using
 [deploy_sdk.py](https://github.com/domokit/mojo/blob/master/sky/tools/deploy_sdk.py)
 Static files (including this README.md) are located under
 [sky/sdk](https://github.com/domokit/mojo/tree/master/sky/sdk).  Pull
 requests and issue reports are glady accepted at the
 [mojo repository](https://github.com/domokit/mojo)!
@@ skipping 91 matching lines @@
 example, you can access the network using the `network_service.mojom` interface.
 Although you can use these low-level interfaces directly, you might prefer to
 access these services via libraries in the framework. For example, the
 `fetch.dart` library wraps the underlying `network_service.mojom` in an
 ergonomic interface:
 
 ```dart
 import 'package:sky/framework/net/fetch.dart';
 
 main() async {
-  Response response = await fetch('example.txt');
+  Response response = await fetchBody('example.txt');
   print(response.bodyAsString());
 }
 ```
 
 Set up your computer
 --------------------
 
 1. Install the Dart SDK:
   - https://www.dartlang.org/tools/download.html
 
@@ skipping 91 matching lines @@
 [Keyboard](https://github.com/domokit/mojo/blob/master/mojo/services/keyboard/public/interfaces/keyboard.mojom)
 service to allow Sky Framework Dart code to interface with the underlying
 platform's Keyboard, but also to expose any additional non-Dart business logic
 to Sky/Dart UI code.
 
 As and example, [SkyApplication](https://github.com/domokit/mojo/blob/master/sky/shell/org/domokit/sky/shell/SkyApplication.java)
 exposes a mojo `network_service` (required by Sky Engine C++ code)
 [SkyDemoApplication](https://github.com/domokit/mojo/blob/master/sky/apk/demo/org/domokit/sky/demo/SkyDemoApplication.java)
 additionally exposes `keyboard_service` and `sensor_service` for use by the Sky
 Framework from Dart.