Allow top-level navigation in extension pop-ups if it only triggers a download.

chrome/browser/prerender/prerender_contents.cc

Index: chrome/browser/prerender/prerender_contents.cc
diff --git a/chrome/browser/prerender/prerender_contents.cc b/chrome/browser/prerender/prerender_contents.cc
index 890008ada304554b0708e70fb887261be35f8afd..a8eaeb8f313d58aaf68b4117660ccd522ae9a161 100644
--- a/chrome/browser/prerender/prerender_contents.cc
+++ b/chrome/browser/prerender/prerender_contents.cc
@@ -112,7 +112,7 @@ class PrerenderContents::WebContentsDelegateImpl
     return NULL;
   }
 
-  bool ShouldTransferNavigation() override {
+  bool ShouldTransferNavigation(bool is_main_frame_navigation) override {
     // Cancel the prerender if the navigation attempts to transfer to a
     // different process.  Examples include server redirects to privileged pages
     // or cross-site subframe navigations in --site-per-process.