In InputMethodMus::DispatchKeyEvent() we temporarily don't send non-char events to IME driver so accelerators work in Mus+ash. This is because we send event acks too early from client to Mus. After we fix this, we should send both char and non-char events to the IME driver.

Some more context follows (I'll do more investigation and make corrections if I misunderstood anything here):

When Mus server sends an event for processing to a client, the clients must notify the Mus server whether they have consumed the event or not (see the comments for OnWindowInputEvent and related functions in //services/ui/public/interfaces/window_tree.mojom).

Mus server uses this information to decide whether to call accelerators (e.g. Ctrl+N for new window) or not.

In the code this happens in NativeWidgetMus::OnWindowInputEvent(). First we try dispatching the event, then set information whether we consumed the event or not.

In implementation of InputMethodMus::DispatchKeyEvent() (see https://codereview.chromium.org/2230393002/), I thought we can do similar to what we are doing in ChromeOS: Send the key events to the input method, and mark them as consumed. If the input method doesn't handle them, then call DispatchKeyEventPostIME() to do post IME processing.

The problem here is that when I mark the key events as consumed, then the code NativeWidgetMus::OnWindowInputEvent() immediately notifies the Mus server that we handled the event, and accelerators are not tried. So, we need to solve this problem.