Rename Container's desiredSize argument to width and height arguments.

Also change SizedBox.

This makes the code that uses Container() and SizedBox() much more readable.

The underlying RenderSizedBox is not affected by this change.

R=abarth@chromium.org, eseidel@chromium.org

Review URL: https://codereview.chromium.org/1166203002

examples/fn2/container.dart

@@ -24,13 +24,13 @@ class ContainerApp extends App {
         new Container(
           padding: new EdgeDims.all(10.0),
           margin: new EdgeDims.all(10.0),
-          desiredSize: new sky.Size(double.INFINITY, 100.0),
+          height: 100.0,
           decoration: new BoxDecoration(backgroundColor: const sky.Color(0xFF00FF00)),
           child: new BlockContainer(
               children: [
                   new Container(
                       decoration: new BoxDecoration(backgroundColor: const sky.Color(0xFFFFFF00)),
-                      desiredSize: new sky.Size(double.INFINITY, 20.0)
+                      height: 20.0,
                   ),
                   new Image(src: "https://www.dartlang.org/logos/dart-logo.png",
                             size: new sky.Size(300.0, 300.0),

examples/stocks2/lib/stock_row.dart

@@ -32,21 +32,21 @@ class StockRow extends Component {
       // ),
       new FlexExpandingChild(new Text(stock.symbol)),
       new Container(
-        desiredSize: const sky.Size.fromWidth(75.0),
+        width: 75.0,
         padding: const EdgeDims.only(right: 16.0),
         // text-align: right
         child: new Text(lastSale)
       ),
       // text-align: right, ${typography.black.caption};
       new SizedBox(
-        desiredSize: const sky.Size.fromWidth(75.0),
+        width: 75.0,
         child: new Text(changeInPrice)
       ),
     ];
 
     return new Container(
       padding: const EdgeDims(16.0, 16.0, 20.0, 16.0),
-      desiredSize: const sky.Size.fromHeight(kHeight),
+      height: kHeight,
       decoration: const BoxDecoration(
         backgroundColor: const sky.Color(0xFFFFFFFF),
         border: const Border(