Enable RenderDecoratedBox to draw borders.

Currently supports only solid borders, but of any colour and size, independently controlling each side.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1154903006

examples/raw/borders.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:math' as math;
+import 'dart:sky' as sky;
+import 'package:sky/framework/app.dart';
+import 'package:sky/framework/rendering/box.dart';
+import 'package:sky/framework/rendering/block.dart';
+import 'package:sky/framework/rendering/node.dart';
+
+AppView app;
+
+void main() {
+
+
+  var root = new RenderBlock(children: [
+    new RenderPadding(
+      padding: new EdgeDims.all(10.0),
+      child: new RenderSizedBox(
+        desiredSize: new sky.Size.fromHeight(100.0),
+        child: new RenderDecoratedBox(
+          decoration: new BoxDecoration(
+            backgroundColor: new sky.Color(0xFFFFFF00)
+          )
+        )
+      )
+    ),
+    new RenderPadding(
+      padding: new EdgeDims.all(10.0),
+      child: new RenderSizedBox(
+        desiredSize: new sky.Size.fromHeight(100.0),
+        child: new RenderDecoratedBox(
+          decoration: new BoxDecoration(
+            border: new Border(
+              top: new BorderSide(color: new sky.Color(0xFFF00000), width: 5.0),
+              right: new BorderSide(color: new sky.Color(0xFFFF9000), width: 10.0),
+              bottom: new BorderSide(color: new sky.Color(0xFFFFF000), width: 15.0),
+              left: new BorderSide(color: new sky.Color(0xFF00FF00), width: 20.0)
+            ),
+            backgroundColor: new sky.Color(0xFFDDDDDD)
+          )
+        )
+      )
+    ),
+    new RenderPadding(
+      padding: new EdgeDims.all(10.0),
+      child: new RenderSizedBox(
+        desiredSize: new sky.Size.fromHeight(100.0),
+        child: new RenderDecoratedBox(
+          decoration: new BoxDecoration(
+            backgroundColor: new sky.Color(0xFFFFFF00)
+          )
+        )
+      )
+    ),
+    new RenderPadding(
+      padding: new EdgeDims.all(10.0),
+      child: new RenderSizedBox(
+        desiredSize: new sky.Size.fromHeight(100.0),
+        child: new RenderDecoratedBox(
+          decoration: new BoxDecoration(
+            backgroundColor: new sky.Color(0xFFFFFF00)
+          )
+        )
+      )
+    ),
+    new RenderPadding(
+      padding: new EdgeDims.all(10.0),
+      child: new RenderSizedBox(
+        desiredSize: new sky.Size.fromHeight(100.0),
+        child: new RenderDecoratedBox(
+          decoration: new BoxDecoration(
+            backgroundColor: new sky.Color(0xFFFFFF00)
+          )
+        )
+      )
+    ),
+  ]);
+  app = new AppView(root);
+}