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

extensions/renderer/resources/guest_view/web_view_attributes.js

Index: extensions/renderer/resources/guest_view/web_view_attributes.js
diff --git a/extensions/renderer/resources/guest_view/web_view_attributes.js b/extensions/renderer/resources/guest_view/web_view_attributes.js
index 88083227b9f0606c1f46792cf24f50f73bc6dc2f..62a6580d6e60014da6d1b2521f0944184299a51c 100644
--- a/extensions/renderer/resources/guest_view/web_view_attributes.js
+++ b/extensions/renderer/resources/guest_view/web_view_attributes.js
@@ -197,6 +197,7 @@ SrcAttribute.prototype.handleMutation = function(oldValue, newValue) {
     // 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.
+    this.observer.takeRecords();

[Fady Samuel, 2014/11/10 18:40:17]

Could you please add a comment explaining why this is necessary. I just can't
remember.

     this.setValueIgnoreMutation(oldValue);
     return;
   }