Convert PrerenderContents to use the new navigation callbacks.

content/public/browser/navigation_handle.h

Index: content/public/browser/navigation_handle.h
diff --git a/content/public/browser/navigation_handle.h b/content/public/browser/navigation_handle.h
index 59114df530208866f1fa92ce4301810f2b0fecfb..0493e024d0c3fe467784505c75e2d609ad0d4ab2 100644
--- a/content/public/browser/navigation_handle.h
+++ b/content/public/browser/navigation_handle.h
@@ -160,6 +160,11 @@ class CONTENT_EXPORT NavigationHandle {
   // Whether the navigation has encountered a server redirect or not.
   virtual bool WasServerRedirect() = 0;
 
+  // Lists the redirects that occurred on the way to the current page. The
+  // current page is the last one in the list (so even when there's no redirect,
+  // there will be one entry in the list).
+  virtual const std::vector<GURL>& GetRedirectChain() = 0;
+
   // Whether the navigation has committed. This returns true for either
   // successful commits or error pages that replace the previous page
   // (distinguished by |IsErrorPage|), and false for errors that leave the user