Add webview sample for captureVisibleRegion().

chrome/common/extensions/docs/examples/api/webview/capturevisibleregion/main.js

Index: chrome/common/extensions/docs/examples/api/webview/capturevisibleregion/main.js
diff --git a/extensions/test/data/platform_app/background.js b/chrome/common/extensions/docs/examples/api/webview/capturevisibleregion/main.js
similarity index 51%
copy from extensions/test/data/platform_app/background.js
copy to chrome/common/extensions/docs/examples/api/webview/capturevisibleregion/main.js
index dccb52cbc8aedb6b5b5a4231b923b5726a40aa21..918162088b2adf9b68bc77e78d50405a4aac740c 100644
--- a/extensions/test/data/platform_app/background.js
+++ b/chrome/common/extensions/docs/examples/api/webview/capturevisibleregion/main.js
@@ -1,12 +1,12 @@
-// Copyright 2014 The Chromium Authors. All rights reserved.
+// Copyright (c) 2016 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.
 
 chrome.app.runtime.onLaunched.addListener(function() {
-  chrome.app.window.create('hello.html', {
-    'innerBounds': {
-      'width': 400,
-      'height': 300
+  chrome.app.window.create('test.html', {
+    innerBounds: {
+      'width': 1280,
+      'height': 800
     }
   });
 });