That would be great! 
Once we support this, we could also make highlighting consistent 
Today it is varying by the key you tap. Examples:
- letter key: dark gray
- number key: light gray
- punctuation (!): none

I think the first step is to have a means to tell the extension if the device is mirroring/casting. Then IME disables hightlight if mirroring and the type if password.
Yingbing, does it make sense?

Another option is chrome decides if password feedback should be given.
Maybe it's better, allowing chrome to implement its own behavior when feedback should be given.

Perhaps a good clean solution for this is to not display the virtual keyboard at all on the secondary device when mirroring or casting, as the keyboard is useful only to the person doing the typing on the primary device.

For a collaboration case, for example, when two or more people are typing into the same textfield that is being viewed by a group, such as taking notes in a meeting, the virtual keyboard for the person casting just gets in the way of everyone else seeing what is going on.

Displaying the virtual keyboard only on the device on which it is being used seems to me like a sensible way to solve both the password-security and the above collaboration issues.

Omri, what do you think?

I test on macOS, they also highlight key on the virtual keyboard.
I agree with rvera@, if we want to improve security.
We should not allow another applications to record the area of the virtual keyboard.

Ping. Omri, I'd like a PM call on this before proceeding. Assigning to you for a response.

Actually, on investigation into the code, it seems that both mirroring and casting happen at the video level, directly using the rendered pixels. In the mirroring case this can even happen in hardware. This means that any kind of differential rendering on the mirrored display isn't going to be possible in all cases. So now I'm back to the original proposal of not highlighting when mirroring/casting and typing a password.

Re comment 6, that would be great in theory, but what I'm scared will happen is that the Virtual Keyboard even if not there will still reduce the real-estate due to moving the page content up which is done when VK is loaded*.

I think the original proposal re comment 10 makes sense as a nice mitigation. We could also not highlight the current character being typed assuming we work on issue 257023.



* this is not true when using floating VK, but that hasn't launched yet.

Internal CL 200494983 fixes this for all cases except the login screen.

I'll leave this open and assigned to me but lower the priority.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/39277d275352023ee99788620580a08dee98e7d4

commit 39277d275352023ee99788620580a08dee98e7d4
Author: Shu Chen <shuchen@google.com>
Date: Mon Dec 10 04:22:51 2018

Propagates the casting & mirroring events from Ash to Chrome.

And pipe the events to the IME extension so that VK can know about it.

Bug: 824656
Change-Id: I680d6faf945c9f74fbeb215662afa9f344293f58
Reviewed-on: https://chromium-review.googlesource.com/c/1362699
Commit-Queue: Shu Chen <shuchen@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615042}
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/ash/ime/ime_controller.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/ash/ime/ime_controller.h
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/ash/ime/test_ime_controller_client.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/ash/ime/test_ime_controller_client.h
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/ash/public/interfaces/ime_controller.mojom
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/ash/shell.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/chromeos/arc/input_method_manager/arc_input_method_manager_service.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/chromeos/input_method/input_method_engine.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/chromeos/input_method/input_method_engine.h
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/chromeos/input_method/input_method_engine_unittest.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/chromeos/input_method/mock_input_method_engine.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/chromeos/input_method/mock_input_method_engine.h
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/extensions/api/input_ime/input_ime_api_chromeos.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/ui/ash/ime_controller_client.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/ui/ash/ime_controller_client.h
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/browser/ui/input_method/input_method_engine_base.h
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/chrome/common/extensions/api/input_method_private.json
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/extensions/browser/extension_event_histogram_value.h
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/tools/metrics/histograms/enums.xml
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/ui/base/ime/chromeos/mock_ime_engine_handler.cc
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/ui/base/ime/chromeos/mock_ime_engine_handler.h
[modify] https://crrev.com/39277d275352023ee99788620580a08dee98e7d4/ui/base/ime/ime_engine_handler_interface.h