Re-land alexbost's experimental offscreenTabs API.

chrome/renderer/resources/extensions/experimental.offscreenTabs_custom_bindings.js

+// Copyright (c) 2012 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.
+
+// Custom bindings for the experimental offscreenTabs API.
+
+(function() {
+
+native function GetChromeHidden();
+
+GetChromeHidden().registerCustomHook(
+    'experimental.offscreenTabs', function(api) {
+  var apiFunctions = api.apiFunctions;
+
+  function maybeCopy(src, prop, dest) {
+    if (src[prop] !== undefined)
+      dest[prop] = src[prop];
+  };
+
+  function keyboardEventFilter(e) {
+    var result = {
+      type: e.type,
+      ctrlKey: e.ctrlKey,
+      shiftKey: e.shiftKey,
+      altKey: e.altKey,
+      metaKey: e.metaKey,
+    };
+    maybeCopy(e, 'keyCode', result);
+    maybeCopy(e, 'charCode', result);
+    return result;
+  };
+
+  function mouseEventFilter(e) {
+    var result = {
+      type: e.type,
+      ctrlKey: e.ctrlKey,
+      shiftKey: e.shiftKey,
+      altKey: e.altKey,
+      metaKey: e.metaKey,
+      button: e.button,
+    };
+    maybeCopy(e, 'wheelDeltaX', result);
+    maybeCopy(e, 'wheelDeltaY', result);
+    return result;
+  };
+
+  // We are making a copy of |arr|, but applying |func| to index 1.
+  function validate(arr, func) {
+    var newArr = [];
+    for (var i = 0; i < arr.length; i++)
+      newArr.push(i == 1 && typeof(arr) == 'object' ? func(arr[i]) : arr[i]);
+    return newArr;
+  }
+
+  apiFunctions.setUpdateArgumentsPreValidate(
+      'sendKeyboardEvent',
+      function() { return validate(arguments, keyboardEventFilter); });
+  apiFunctions.setUpdateArgumentsPreValidate(
+      'sendMouseEvent',
+      function() { return validate(arguments, mouseEventFilter); });
+});
+
+})();