Implement a basic IME-aware input element

This CL introduces a new keyboard service that understands Android IME and
starts work on a Input component that interacts with this service to provide an
editing control.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/995613002

examples/editor/editor_app.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 '../../framework/fn.dart';
+import 'input.dart';
+
+class EditorApp extends App {
+  Node build() {
+    return new Input();
+  }
+}

examples/editor/index.sky

+#!mojo mojo:sky_viewer
+<sky>
+<import src="/sky/framework/debug/shake-to-reload.sky" />
+<script>
+import 'editor_app.dart';
+main() {
+  new EditorApp();
+}
+</script>
+</sky>

examples/editor/input.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 '../../framework/fn.dart';
+import '../../framework/shell.dart' as shell;
+import 'package:sky/services/keyboard/keyboard.mojom.dart';
+import 'dart:math';
+
+class Input extends Component implements KeyboardClient{
+  static Style _style = new Style('''
+    display: paragraph;
+    padding: 10px;
+    height: 200px;
+    background-color: lightblue;'''
+  );
+
+  static Style _composingStyle = new Style('''
+    display: inline;
+    text-decoration: underline;'''
+  );
+
+  KeyboardServiceProxy _service;
+  KeyboardClientStub _stub;
+
+  String _text = "";
+  int _composingStart = -1;
+  int _composingEnd = -1;
+
+  Input({Object key}) : super(key: key, stateful: true) {
+    events.listen('click', _handleClick);
+    _stub = new KeyboardClientStub.unbound()..impl = this;
+  }
+
+  bool get _hasComposingRegion => _composingStart != -1 && _composingEnd != -1;
+
+  void _handleClick(_) {
+    if (_service != null)
+      return;
+    _service = new KeyboardServiceProxy.unbound();
+    shell.requestService(_service);
+    _service.ptr.show(_stub);
+  }
+
+  void _replaceComposing(String text) {
+    if (!_hasComposingRegion) {
+      _composingStart = _text.length;
+      _composingEnd = _composingStart + text.length;
+      _text += text;
+      return;
+    }
+
+    _text = _text.substring(0, _composingStart)
+        + text + _text.substring(_composingEnd);
+    _composingEnd = _composingStart + text.length;
+  }
+
+  void _clearComposingRegion() {
+    _composingStart = -1;
+    _composingEnd = -1;
+  }
+
+  void commitText(String text, int newCursorPosition) {
+    setState(() {
+      _replaceComposing(text);
+      _clearComposingRegion();
+    });
+  }
+
+  void setComposingText(String text, int newCursorPosition) {
+    setState(() {
+      _replaceComposing(text);
+    });
+  }
+
+  void setComposingRegion(int start, int end) {
+    setState(() {
+      _composingStart = start;
+      _composingEnd = end;
+    });
+  }
+
+  Node build() {
+    List<Node> children = new List<Node>();
+
+    if (!_hasComposingRegion) {
+      children.add(new Text(_text));
+    } else {
+      String run = _text.substring(0, _composingStart);
+      if (!run.isEmpty)
+        children.add(new Text(run));
+
+      run = _text.substring(_composingStart, _composingEnd);
+      if (!run.isEmpty) {
+        children.add(new Container(
+          style: _composingStyle,
+          children: [new Text(_text.substring(_composingStart, _composingEnd))]
+        ));
+      }
+
+      run = _text.substring(_composingEnd);
+      if (!run.isEmpty)
+        children.add(new Text(_text.substring(_composingEnd)));
+    }
+
+    return new Container(
+      style: _style,
+      children: children
+    );
+  }
+}