OS: Chrome OS

What steps will reproduce the problem?
(1) Enable and switch US international/Dvorak/Colemak keyboard;
(2) press AltGr key (followed by Shift key for an additional layer);
(3) Observe on-screen virtual keyboard.

What is the expected result?
Every soft key, including those in AltGr+Shift layer should be assigned a character;

What happens instead?
Some keys are blank.

Discussion:

First we want to complete the table of characters in AltGr layer, follow that of US international keyboard on Linux;

For keys that is unassigned with characters in ALtGr layer, fall back to the character in the base layer;

For non-Qwerty layouts, rearrange the completed AltGr layer by following the base layer layout.