Sticky keys modifies an entire scroll sequence instead of just a single event.

ash/wm/sticky_keys.h

Index: ash/wm/sticky_keys.h
diff --git a/ash/wm/sticky_keys.h b/ash/wm/sticky_keys.h
index 7b8f6f1deecfa624207264783c8b01e90cb39a90..1a2789214bbfb46af8ec4b1a3bf2e7cd662c36c1 100644
--- a/ash/wm/sticky_keys.h
+++ b/ash/wm/sticky_keys.h
@@ -222,6 +222,11 @@ class ASH_EXPORT StickyKeysHandler {
   // the ENABLED state.
   bool preparing_to_enable_;
 
+  // Tracks the scroll direction of the current scroll sequence. Sticky keys
+  // stops modifying the scroll events of the sequence when the direction
+  // changes. If no sequence is tracked, the value is 0.
+  int scroll_delta_;
+
   // The modifier up key event to be sent on non modifier key on ENABLED state.
   scoped_ptr<ui::KeyEvent> modifier_up_event_;