weidongg, here's another shortcut-related bug. please take a look. Thanks.

The logic is handled by RewriteModifierKeys (https://cs.chromium.org/chromium/src/ui/chromeos/events/event_rewriter_chromeos.cc?l=808-824). The input parameter key_event only includes two types of key event: ET_KEY_PRESSED and ET_KEY_RELEASED. IMO, use a static variable to record the previous key_evennt:
Press->Press: ignore
Press->Release: ignore
Null/Release->Press: Toggle CAPS_LOCK

Try checking for the flag EF_IS_REPEAT [1]. What do you get?

[1]: https://cs.chromium.org/chromium/src/ui/events/event_constants.h?l=124

This flag is set at the constructor of KeyEvent (https://cs.chromium.org/chromium/src/ui/events/event.cc?l=1138).And it's decided by IsRepeated (https://cs.chromium.org/chromium/src/ui/events/event.cc?l=1098) which always returns false when Caps Lock is held down.

I don't think ignoring keys with REPEAT turned on is the right fix. For example, if you keep holding down the volume up/down keys, you should expect the repeat-keys to actually continue to change the volume level, right?

When a key is pressed, KeyboardEvdev::DispatchKey will receive the key along with a 'repeat[1]'. Why KeyEvent[2] does not use this repeat in its constructor, rather than use its own IsRepeat?

[1] https://cs.chromium.org/chromium/src/ui/events/ozone/evdev/keyboard_evdev.cc?l=225&gsn=repeat
[2] https://cs.chromium.org/chromium/src/ui/events/ozone/evdev/keyboard_evdev.cc?gsn=modifier_flags_&l=242
[3] https://cs.chromium.org/chromium/src/ui/events/event.cc?gsn=KeyEvent&l=1098

Initial State: Caps Lock is disabled

Action: Hold down ESC which is remapped to Caps Lock

Flow:
1. KeyBoardEvdev[1] use received ESC key and modifier_flags_(a static variable) to create KeyEvent (flags_=modifier_flags_, key_code_=VKEY_ESCAPE).
2. In KeyEvent constructor, It check if itself is repeated. If the flags_ of current KeyEvent is the same as previous one, then EF_IS_REPEAT bit of flags_ is set.
3. KeyEvent is dispatched to RewriteKeyEvent which discards the KeyEvent if its EF_IS_REPEAT bit of flags_ is set.
4. If KeyEvent is not discarded, RewriteKeyEvent sends KeyEvent to RewriteModifierKeys which rewrite ESC key to Caps Lock key.
5. RewriteModifierKeys toggles Caps Lock and toggles modifier_flags_

Problem:
1. When I hold down ESC, KeyBoardEvdev keeps creating KeyEvent.
2. Before the first KeyEvent, modifier_flags_ is 0x0 which means the first KeyEvent’s flags_ is 0x0. But there’s no previous KeyEvent, so EF_IS_REPEAT is not set. So RewriteKeyEvent doesn't discard the KeyEvent.
3. RewriteModifierKeys turns on Caps Lock and set modifier_flags_ to 0x100
4. The second KeyEvent’s flag_ is set to 0x100 in the constructor. It’s different from the first KeyEvent’s flag_ which is 0x0, so EF_IS_REPEAT is not set.
5. RewriteModifierKeys turns off Caps Lock and set modifier_flags_ to 0x0
6.  The third KeyEvent’s flag_ is set to 0x0 in the constructor.  It’s different from the second KeyEvent’s flag_ which is 0x100, so EF_IS_REPEAT is not set.
7. RewriteModifierKeys turns on Caps Lock and set modifier_flags_ to 0x100
…… So on so forth, that’s why Caps Lock keeps toggling.


[1]https://cs.chromium.org/chromium/src/ui/events/ozone/evdev/keyboard_evdev.cc?gsn=modifier_flags_&l=223

Besides Caps Lock, Num Lock and Scroll Lock also has this problem. 
IMO, potential solutions include:
1. Treat Caps Lock/ Num Lock/Scroll Lock as special case in IsRepeat function of KeyEvent, but the problem is that Caps Lock is possibly remapped. The remapping occurs at RewriteModifierKeys which happens after IsRepeat, so IsRepeat doesn't recognize Caps Lock key.
2. Self-maintain a flag to record the previous Caps Lock press in RewriteModifierKeys, like the first patch of https://codereview.chromium.org/2763483002/#ps1.
3. Or KeyEvent maintains and expose a last_key_event, so that RewriteModifierKeys can use it to track the previous key event.

What do you think @sadrul?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/863b0d4dbe21b493e2dfa59c6d52e02a1af73565

commit 863b0d4dbe21b493e2dfa59c6d52e02a1af73565
Author: weidongg <weidongg@chromium.org>
Date: Thu Apr 13 19:23:10 2017

Fix Caps Lock bug

Move the handling of Caps Lock key event to accelerator controller and trigger toggling on key-release. Remove the handling code of Caps Lock for X11 from InputMethodChromeOS::DispatchKeyEvent, because it is now handled only in accelerator controller. This should also work for both x11+ozone environment and x11 environment on desktop.

BUG= 700705 

Review-Url: https://codereview.chromium.org/2763483002
Cr-Commit-Position: refs/heads/master@{#464499}

[modify] https://crrev.com/863b0d4dbe21b493e2dfa59c6d52e02a1af73565/ash/accelerators/accelerator_controller.cc
[modify] https://crrev.com/863b0d4dbe21b493e2dfa59c6d52e02a1af73565/ash/accelerators/accelerator_controller_unittest.cc
[modify] https://crrev.com/863b0d4dbe21b493e2dfa59c6d52e02a1af73565/ash/accelerators/accelerator_table.cc
[modify] https://crrev.com/863b0d4dbe21b493e2dfa59c6d52e02a1af73565/ash/accelerators/accelerator_table_unittest.cc
[modify] https://crrev.com/863b0d4dbe21b493e2dfa59c6d52e02a1af73565/chrome/browser/chromeos/events/event_rewriter_unittest.cc
[modify] https://crrev.com/863b0d4dbe21b493e2dfa59c6d52e02a1af73565/ui/base/ime/input_method_chromeos.cc
[modify] https://crrev.com/863b0d4dbe21b493e2dfa59c6d52e02a1af73565/ui/chromeos/events/event_rewriter_chromeos.cc

9534.0.0, 60.0.3092.0