Clean up event flags a bit:

ui/events/event_constants.h

Index: ui/events/event_constants.h
diff --git a/ui/events/event_constants.h b/ui/events/event_constants.h
index 70fdb7283f6fcd4a1491dc6fb626b1466eb4b897..623f5a5c8853f2a8ce4515a7c46ad63a24c1f3e6 100644
--- a/ui/events/event_constants.h
+++ b/ui/events/event_constants.h
@@ -73,49 +73,58 @@ enum EventType {
   ET_LAST
 };
 
-// Event flags currently supported
+// Event flags currently supported.  It is OK to add values to the middle of
+// this list and/or reorder it, but make sure you also touch the various other
+// enums/constants that want to stay in sync with this.
 enum EventFlags {
   EF_NONE                 = 0,       // Used to denote no flags explicitly
-  EF_CAPS_LOCK_DOWN       = 1 << 0,
+
+  // Universally applicable status bits.
+  EF_IS_SYNTHESIZED       = 1 << 0,
+
+  // Modifier key state.
   EF_SHIFT_DOWN           = 1 << 1,
   EF_CONTROL_DOWN         = 1 << 2,
   EF_ALT_DOWN             = 1 << 3,
-  EF_LEFT_MOUSE_BUTTON    = 1 << 4,
-  EF_MIDDLE_MOUSE_BUTTON  = 1 << 5,
-  EF_RIGHT_MOUSE_BUTTON   = 1 << 6,
-  EF_COMMAND_DOWN         = 1 << 7,  // GUI Key (e.g. Command on OS X
+  EF_COMMAND_DOWN         = 1 << 4,  // GUI Key (e.g. Command on OS X
                                      // keyboards, Search on Chromebook
                                      // keyboards, Windows on MS-oriented
                                      // keyboards)
-  EF_EXTENDED             = 1 << 8,  // Windows extended key (see WM_KEYDOWN
-                                     // doc)
-  EF_IS_SYNTHESIZED       = 1 << 9,
-  EF_ALTGR_DOWN           = 1 << 10,
-  EF_MOD3_DOWN            = 1 << 11,
-  EF_BACK_MOUSE_BUTTON    = 1 << 12,
-  EF_FORWARD_MOUSE_BUTTON = 1 << 13,
-  EF_NUM_LOCK_DOWN        = 1 << 14,
-  EF_SCROLL_LOCK_DOWN     = 1 << 15,
+  EF_ALTGR_DOWN           = 1 << 5,
+  EF_MOD3_DOWN            = 1 << 6,
+
+  // Other keyboard state.
+  EF_NUM_LOCK_ON          = 1 << 7,
+  EF_CAPS_LOCK_ON         = 1 << 8,
+  EF_SCROLL_LOCK_ON       = 1 << 9,
+
+  // Mouse buttons.
+  EF_LEFT_MOUSE_BUTTON    = 1 << 10,
+  EF_MIDDLE_MOUSE_BUTTON  = 1 << 11,
+  EF_RIGHT_MOUSE_BUTTON   = 1 << 12,
+  EF_BACK_MOUSE_BUTTON    = 1 << 13,
+  EF_FORWARD_MOUSE_BUTTON = 1 << 14,
 };
 
 // Flags specific to key events
 enum KeyEventFlags {
-  EF_IME_FABRICATED_KEY = 1 << 16,  // Key event fabricated by the underlying
+  EF_IME_FABRICATED_KEY = 1 << 15,  // Key event fabricated by the underlying
                                     // IME without a user action.
                                     // (Linux X11 only)
-  EF_IS_REPEAT          = 1 << 17,
-  EF_FINAL              = 1 << 18,  // Do not remap; the event was created with
+  EF_IS_REPEAT          = 1 << 16,
+  EF_FINAL              = 1 << 17,  // Do not remap; the event was created with
                                     // the desired final values.
+  EF_IS_EXTENDED_KEY    = 1 << 18,  // Windows extended key (see WM_KEYDOWN doc)
 };
 
 // Flags specific to mouse events
 enum MouseEventFlags {
-  EF_IS_DOUBLE_CLICK     = 1 << 16,
-  EF_IS_TRIPLE_CLICK     = 1 << 17,
-  EF_IS_NON_CLIENT       = 1 << 18,
-  EF_FROM_TOUCH          = 1 << 19,  // Indicates this mouse event is generated
+  EF_IS_DOUBLE_CLICK     = 1 << 15,
+  EF_IS_TRIPLE_CLICK     = 1 << 16,
+  EF_IS_NON_CLIENT       = 1 << 17,
+  EF_FROM_TOUCH          = 1 << 18,  // Indicates this mouse event is generated
                                      // from an unconsumed touch/gesture event.
-  EF_TOUCH_ACCESSIBILITY = 1 << 20,  // Indicates this event was generated from
+  EF_TOUCH_ACCESSIBILITY = 1 << 19,  // Indicates this event was generated from
                                      // touch accessibility mode.
 };