alternate ntp: implement Show/HideBars API to reduce jank when showing/hiding bars

chrome/common/search_types.h

Index: chrome/common/search_types.h
diff --git a/chrome/common/search_types.h b/chrome/common/search_types.h
index 04d64b6564e56fcd3eb86ce20f9ebc4b00304918..5fb85e753c0e1840c52c4889d57f576325fbfd3f 100644
--- a/chrome/common/search_types.h
+++ b/chrome/common/search_types.h
@@ -50,6 +50,10 @@ struct Mode {
     return mode == rhs.mode && origin == rhs.origin;
   }
 
+  bool operator!=(const Mode& rhs) const {
+    return !(*this == rhs);
+  }
+
   bool is_default() const {
     return mode == MODE_DEFAULT;
   }