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

ash/wm/sticky_keys.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/wm/sticky_keys.h"
 
 #if defined(USE_X11)
 #include <X11/extensions/XInput2.h>
 #include <X11/Xlib.h>
 #undef RootWindow
@@ skipping 154 matching lines @@
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 //  StickyKeysHandler
 StickyKeysHandler::StickyKeysHandler(ui::EventFlags target_modifier_flag,
                                      StickyKeysHandlerDelegate* delegate)
     : modifier_flag_(target_modifier_flag),
       current_state_(DISABLED),
       event_from_myself_(false),
       preparing_to_enable_(false),
+      scroll_delta_(0),
       delegate_(delegate) {
 }
 
 StickyKeysHandler::~StickyKeysHandler() {
 }
 
 StickyKeysHandler::StickyKeysHandlerDelegate::StickyKeysHandlerDelegate() {
 }
 
 StickyKeysHandler::StickyKeysHandlerDelegate::~StickyKeysHandlerDelegate() {
@@ skipping 31 matching lines @@
     return true;
   }
 
   return false;
 }
 
 bool StickyKeysHandler::HandleScrollEvent(ui::ScrollEvent* event) {
   if (event_from_myself_ || current_state_ == DISABLED)
     return false;
   DCHECK(current_state_ == ENABLED || current_state_ == LOCKED);
+  preparing_to_enable_ = false;
 
-  preparing_to_enable_ = false;
-  AppendModifier(event);
-  if (current_state_ == ENABLED) {
+  // We detect a direction change if the current |scroll_delta_| is assigned
+  // and the offset of the current scroll event has the opposing sign.
+  bool direction_changed = false;
+  if (current_state_ == ENABLED && event->type() == ui::ET_SCROLL) {
+    int offset = event->y_offset();
+    if (scroll_delta_)
+      direction_changed = offset * scroll_delta_ <= 0;
+    scroll_delta_ = offset;
+  }
+
+  if (!direction_changed)
+    AppendModifier(event);
+
+  // We want to modify all the scroll events in the scroll sequence, which ends
+  // with a fling start event. We also stop when the scroll sequence changes
+  // direction.
+  if (current_state_ == ENABLED &&
+      (event->type() == ui::ET_SCROLL_FLING_START || direction_changed)) {
     current_state_ = DISABLED;
+    scroll_delta_ = 0;
     DispatchEventAndReleaseModifier(event);
     return true;
   }
 
   return false;
 }
 
 StickyKeysHandler::KeyEventType
     StickyKeysHandler::TranslateKeyEvent(ui::KeyEvent* event) {
   bool is_target_key = false;
@@ skipping 20 matching lines @@
   }
   return event->type() == ui::ET_KEY_PRESSED ?
       OTHER_MODIFIER_DOWN : OTHER_MODIFIER_UP;
 }
 
 bool StickyKeysHandler::HandleDisabledState(ui::KeyEvent* event) {
   switch (TranslateKeyEvent(event)) {
     case TARGET_MODIFIER_UP:
       if (preparing_to_enable_) {
         preparing_to_enable_ = false;
+        scroll_delta_ = 0;
         current_state_ = ENABLED;
         modifier_up_event_.reset(event->Copy());
         return true;
       }
       return false;
     case TARGET_MODIFIER_DOWN:
       preparing_to_enable_ = true;
       return false;
     case NORMAL_KEY_DOWN:
       preparing_to_enable_ = false;
@@ skipping 137 matching lines @@
           &xievent->mods.effective));
     }
   }
 #elif defined(USE_OZONE)
   NOTIMPLEMENTED() << "Modifier key is not handled";
 #endif
   event->set_flags(event->flags() | modifier_flag_);
 }
 
 }  // namespace ash