Don't calculate a shown ratio when top controls height is 0.

cc/input/top_controls_manager.cc

Index: cc/input/top_controls_manager.cc
diff --git a/cc/input/top_controls_manager.cc b/cc/input/top_controls_manager.cc
index 7362805de99acba4c5caa3145f9f268df1778336..3ac3b4a8813cfcf733cea0f6449817e1acf733f7 100644
--- a/cc/input/top_controls_manager.cc
+++ b/cc/input/top_controls_manager.cc
@@ -104,6 +104,9 @@ gfx::Vector2dF TopControlsManager::ScrollBy(
   if (pinch_gesture_active_)
     return pending_delta;
 
+  if (!TopControlsHeight())
+    return pending_delta;
+
   if (permitted_state_ == SHOWN && pending_delta.y() > 0)
     return pending_delta;
   else if (permitted_state_ == HIDDEN && pending_delta.y() < 0)