chrome: Cleanup class/struct forward declarations

chrome/browser/ui/hung_plugin_tab_helper.h

Index: chrome/browser/ui/hung_plugin_tab_helper.h
diff --git a/chrome/browser/ui/hung_plugin_tab_helper.h b/chrome/browser/ui/hung_plugin_tab_helper.h
index e737ec16fe829f02348cd500f9e5be984d8c78a3..4eb7eeace633979e2b970c0574af137f0f438fc2 100644
--- a/chrome/browser/ui/hung_plugin_tab_helper.h
+++ b/chrome/browser/ui/hung_plugin_tab_helper.h
@@ -21,10 +21,6 @@ namespace base {
 class FilePath;
 }
 
-namespace infobars {
-class InfoBarDelegate;
-}
-
 // Manages per-tab state with regard to hung plugins. This only handles
 // Pepper plugins which we know are windowless. Hung NPAPI plugins (which
 // may have native windows) can not be handled with infobars and have a