Got rid of the internal copies of webview attributes.

extensions/renderer/resources/guest_view/web_view_attributes.js

 // Copyright (c) 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.
 
 // This module implements the attributes of the <webview> tag.
 
 var WebView = require('webView').WebView;
 var WebViewConstants = require('webViewConstants').WebViewConstants;
 
 // -----------------------------------------------------------------------------
 // Attribute objects.
 
 // Default implementation of a WebView attribute.
 function WebViewAttribute(name, webViewImpl) {
   this.name = name;
-  this.value = '';
   this.webViewImpl = webViewImpl;
+  this.ignoreNextMutation = false;
 }
 
+// Retrieves and returns the attribute's value.
 WebViewAttribute.prototype.getValue = function() {
-  return this.value || '';
+  return this.webViewImpl.webviewNode.getAttribute(this.name);
 };
 
+// Sets the attribute's value.
 WebViewAttribute.prototype.setValue = function(value) {
-  this.value = value;
+  this.webViewImpl.webviewNode.setAttribute(this.name, !value ? '' : value);
 };
 
+// Called when the attribute's value changes.
+WebViewAttribute.prototype.handleMutation = function() {}
+
+// Attribute specifying whether transparency is allowed in the webview.
+function BooleanAttribute(name, webViewImpl) {
+  WebViewAttribute.call(this, name, webViewImpl);
+}
+
+BooleanAttribute.prototype = new WebViewAttribute();
+
+BooleanAttribute.prototype.getValue = function() {
+  // This attribute is treated as a boolean, and is retrieved as such.
+  return this.webViewImpl.webviewNode.hasAttribute(this.name);
+}
+
+BooleanAttribute.prototype.setValue = function(value) {
+  if (!value) {
+    this.webViewImpl.webviewNode.removeAttribute(this.name);
+  } else {
+    this.webViewImpl.webviewNode.setAttribute(this.name, '');
+  }
+}
+
 // Attribute representing the state of the storage partition.
 function Partition(webViewImpl) {
+  WebViewAttribute.call(this,
+                        WebViewConstants.ATTRIBUTE_PARTITION,
+                        webViewImpl);
   this.validPartitionId = true;
   this.persistStorage = false;
   this.storagePartitionId = '';
-  this.webViewImpl = webViewImpl;
 }
 
-Partition.prototype = new WebViewAttribute(
-    WebViewConstants.ATTRIBUTE_PARTITION);
+Partition.prototype = new WebViewAttribute();
 
-Partition.prototype.getValue = function() {
-  if (!this.validPartitionId) {
-    return '';
+Partition.prototype.handleMutation = function(oldValue, newValue) {
+  newValue = newValue || '';
+
+  // Set |persistStorage| and |storagePartitionId| from |newValue|.
+  var LEN = 'persist:'.length;
+  this.persistStorage = newValue.substr(0, LEN) == 'persist:';
+  this.storagePartitionId = this.persistStorage ? newValue.substr(LEN) :
+      newValue;

[Fady Samuel, 2014/11/03 22:38:18]

It doesn't seem like you need both persistStorage and storagePartitionId. 

[paulmeyer, 2014/11/03 22:58:19]

Done.

+
+  // The partition cannot change if the webview has already navigated.
+  if (!this.webViewImpl.beforeFirstNavigation) {
+    window.console.error(WebViewConstants.ERROR_MSG_ALREADY_NAVIGATED);
+    this.ignoreNextMutation = true;
+    this.webViewImpl.webviewNode.setAttribute(this.name, oldValue);
+    return;
   }
-  return (this.persistStorage ? 'persist:' : '') + this.storagePartitionId;
-};
-
-Partition.prototype.setValue = function(value) {
-  var result = {};
-  var hasNavigated = !this.webViewImpl.beforeFirstNavigation;
-  if (hasNavigated) {
-    result.error = WebViewConstants.ERROR_MSG_ALREADY_NAVIGATED;
-    return result;
+  if (newValue == 'persist:') {
+    this.validPartitionId = false;
+    window.console.error(
+        WebViewConstants.ERROR_MSG_INVALID_PARTITION_ATTRIBUTE);
   }
-  if (!value) {
-    value = '';
-  }
-
-  var LEN = 'persist:'.length;
-  if (value.substr(0, LEN) == 'persist:') {
-    value = value.substr(LEN);
-    if (!value) {
-      this.validPartitionId = false;
-      result.error = WebViewConstants.ERROR_MSG_INVALID_PARTITION_ATTRIBUTE;
-      return result;
-    }
-    this.persistStorage = true;
-  } else {
-    this.persistStorage = false;
-  }
-
-  this.storagePartitionId = value;
-  return result;
-};
+}
 
 // -----------------------------------------------------------------------------
 
 // Sets up all of the webview attributes.
 WebView.prototype.setupWebViewAttributes = function() {
   this.attributes = {};
 
   // Initialize the attributes with special behavior (and custom attribute
   // objects).
+  this.attributes[WebViewConstants.ATTRIBUTE_ALLOWTRANSPARENCY] =
+      new BooleanAttribute(WebViewConstants.ATTRIBUTE_ALLOWTRANSPARENCY, this);
+  this.attributes[WebViewConstants.ATTRIBUTE_AUTOSIZE] =
+      new BooleanAttribute(WebViewConstants.ATTRIBUTE_AUTOSIZE, this);
   this.attributes[WebViewConstants.ATTRIBUTE_PARTITION] = new Partition(this);
 
   // Initialize the remaining attributes, which have default behavior.
-  var defaultAttributes = [WebViewConstants.ATTRIBUTE_ALLOWTRANSPARENCY,
-                           WebViewConstants.ATTRIBUTE_AUTOSIZE,
-                           WebViewConstants.ATTRIBUTE_MAXHEIGHT,
+  var defaultAttributes = [WebViewConstants.ATTRIBUTE_MAXHEIGHT,
                            WebViewConstants.ATTRIBUTE_MAXWIDTH,
                            WebViewConstants.ATTRIBUTE_MINHEIGHT,
                            WebViewConstants.ATTRIBUTE_MINWIDTH,
                            WebViewConstants.ATTRIBUTE_NAME,
                            WebViewConstants.ATTRIBUTE_SRC];
   for (var i = 0; defaultAttributes[i]; ++i) {
     this.attributes[defaultAttributes[i]] =
         new WebViewAttribute(defaultAttributes[i], this);
   }
 };