Fixed the problem at the source of the flaky WebViewTest.ShimArcAttribute test.

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 GuestViewInternal =
     require('binding').Binding.create('guestViewInternal').generate();
 var WebViewImpl = require('webView').WebViewImpl;
 var WebViewConstants = require('webViewConstants').WebViewConstants;
@@ skipping 179 matching lines @@
 SrcAttribute.prototype.__proto__ = WebViewAttribute.prototype;
 
 SrcAttribute.prototype.handleMutation = function(oldValue, newValue) {
   // Once we have navigated, we don't allow clearing the src attribute.
   // Once <webview> enters a navigated state, it cannot return to a
   // placeholder state.
   if (!newValue && oldValue) {
     // src attribute changes normally initiate a navigation. We suppress
     // the next src attribute handler call to avoid reloading the page
     // on every guest-initiated navigation.
+    // takeRecords() needed to clear queued up src mutations.

[Fady Samuel, 2014/11/10 19:25:39]

This doesn't explain why this was causing an issue. Could you add further
clarification?

[paulmeyer, 2014/11/10 19:35:48]

Done.

+    this.observer.takeRecords();
     this.setValueIgnoreMutation(oldValue);
     return;
   }
   this.webViewImpl.parseSrcAttribute();
 };
 
 // The purpose of this mutation observer is to catch assignment to the src
 // attribute without any changes to its value. This is useful in the case
 // where the webview guest has crashed and navigating to the same address
 // spawns off a new process.
@@ skipping 36 matching lines @@
 
   var autosizeAttributes = [WebViewConstants.ATTRIBUTE_MAXHEIGHT,
                             WebViewConstants.ATTRIBUTE_MAXWIDTH,
                             WebViewConstants.ATTRIBUTE_MINHEIGHT,
                             WebViewConstants.ATTRIBUTE_MINWIDTH];
   for (var i = 0; autosizeAttributes[i]; ++i) {
     this.attributes[autosizeAttributes[i]] =
         new AutosizeDimensionAttribute(autosizeAttributes[i], this);
   }
 };