Add a simple inksplash example

We'll eventually turn this into a full fn2 component, but for now it's just an
example.

To make this work, I created a schedule.dart as a start to implementing
scheduler.md. For now, I've kept the API similar to the web platform so that
the old world can continue use it backed by sky.window.requestAnimationFrame.

R=eseidel@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1145973009

examples/raw/ink_well.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 'dart:sky' as sky;
+import 'package:sky/framework/app.dart';
+import 'package:sky/framework/rendering/render_box.dart';
+import 'package:sky/framework/rendering/render_node.dart';
+import 'package:sky/framework/animation/animated_value.dart';
+import 'package:sky/framework/animation/curves.dart';
+
+const double _kInitialSize = 0.0;
+const double _kTargetSize = 100.0;
+const double _kSplashDuration = 500.0;
+const int _kInitialOpacity = 0x80;
+
+class InkSplash {
+  final InkWell inkWell;
+  final sky.Paint _paint = new sky.Paint();
+  final sky.Point position;
+  AnimatedValue radius;
+
+  InkSplash({ this.position, this.inkWell }) {
+    radius = new AnimatedValue(_kInitialSize, onChange: _handleRadiusChange);
+    radius.animateTo(_kTargetSize, _kSplashDuration, curve: easeOut);
+  }
+
+  void _handleRadiusChange() {
+    if (radius.value == _kTargetSize)
+      inkWell._splashes.remove(this);
+    inkWell.markNeedsPaint();
+  }
+
+  void paint(RenderNodeDisplayList canvas) {
+    int opacity = (_kInitialOpacity * (1.0 - (radius.value / _kTargetSize))).floor();
+    _paint.color = opacity << 24;
+    canvas.drawCircle(position.x, position.y, radius.value, _paint);
+  }
+}
+
+class InkWell extends RenderBox {
+  final List<InkSplash> _splashes = new List<InkSplash>();
+
+  void handlePointer(sky.PointerEvent event) {
+    switch (event.type) {
+      case 'pointerdown':
+        _splashes.add(new InkSplash(position: new sky.Point(event.x, event.y),
+                                    inkWell: this));
+        break;
+    }
+    markNeedsPaint();
+  }
+
+  void performLayout() {
+    size = constraints.constrain(new sky.Size.infinite());
+  }
+
+  void paint(RenderNodeDisplayList canvas) {
+    canvas.drawRect(new sky.Rect.fromLTRB(0.0, 0.0, size.width, size.height),
+                    new sky.Paint()..color = 0xFFCCCCCC);
+    for (InkSplash splash in _splashes)
+      splash.paint(canvas);
+  }
+}
+
+AppView app;
+
+void main() {
+  app = new AppView(new InkWell());
+}

examples/raw/touch_demo.dart

@@ -61,6 +61,10 @@ class RenderTouchDemo extends RenderBox {
     markNeedsPaint();
   }
 
+  void performLayout() {
+    size = constraints.constrain(new Size.infinite());
+  }
+
   void paint(RenderNodeDisplayList canvas) {
     dots.forEach((_, Dot dot) {
       dot.paint(canvas);