Add support for omnibox.onInputStarted and onInputCancelled.

chrome/browser/autocomplete/autocomplete.h

Index: chrome/browser/autocomplete/autocomplete.h
diff --git a/chrome/browser/autocomplete/autocomplete.h b/chrome/browser/autocomplete/autocomplete.h
index 2338846c468c46ea342fbef5fd1d05c1d62185dd..9cfb1b4f8b5f4031f3ee5ca48d25eae3673b519b 100644
--- a/chrome/browser/autocomplete/autocomplete.h
+++ b/chrome/browser/autocomplete/autocomplete.h
@@ -528,7 +528,8 @@ class AutocompleteProvider
                      bool minimal_changes) = 0;
 
   // Called when a provider must not make any more callbacks for the current
-  // query.
+  // query. This will be called regardless of whether the provider is already
+  // done.
   virtual void Stop() {
     done_ = true;
   }