Fix SetShape (SetAlphaShape) to allow Null regions (+ tests).

chrome/test/data/extensions/platform_apps/windows_api_shape/background.js

+// Copyright 2014 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.
+
+function testWindowShape(testId, region) {
+  var createOptions = { id: testId, frame: 'none' };
+
+  chrome.app.window.create('index.html',
+                           createOptions,
+                           chrome.test.callbackPass(function(win) {
+      win.setShape(region)
+  }));
+}
+
+chrome.app.runtime.onLaunched.addListener(function() {
+  chrome.test.runTests([
+
+    // Window shape is a single rect.
+    function testWindowShapeSingleRect() {
+      testWindowShape('testWindowShapeSingleRect',
+                      {rects: [{left:100, top:50, width:50, height:100}]});
+    },
+
+    // Window shape is multiple rects.
+    function testWindowShapeMultipleRects() {
+      testWindowShape('testWindowShapeMultipleRects',
+                      {rects: [{left:100, top:50, width:50, height:100},
+                               {left:200, top:100, width:50, height:50}]});
+    },
+
+    // Window shape is null.
+    function testWindowShapeNull() {
+      testWindowShape('testWindowShapeNull', {});
+    },
+
+    // Window shape is empty.
+    function testWindowShapeEmpty() {
+      testWindowShape('testWindowShapeEmpty', {rects: []});
+    },
+
+  ]);
+});