Deflake and add more prerender_browsertests focused on back navigation.

chrome/test/data/prerender/prerender_page_with_link.html

Index: chrome/test/data/prerender/prerender_page_with_link.html
===================================================================
--- chrome/test/data/prerender/prerender_page_with_link.html	(revision 98079)
+++ chrome/test/data/prerender/prerender_page_with_link.html	(working copy)
@@ -5,17 +5,19 @@
 <script>
 var pageWasPrerendered = false;
 
-// Make sure plugin was not loaded while prerendering.
 function DidPrerenderPass() {
   pageWasPrerendered = true;
   return true;
 }
 
+function DidDisplayPass() {
+  return pageWasPrerendered;
+}
+
 function ClickOpenLink() {
   var eventObject = document.createEvent('MouseEvents');
   eventObject.initMouseEvent('click');
   document.getElementById('toClick').dispatchEvent(eventObject);
-  return true;
 }
 
 function IsOriginalPrerenderPage() {