hterm: terminal: document why we don't use realizeSize helper
hterm: terminal: document why we don't use realizeSize helper

This looks like an "obvious" place to optimize, but that would be
incorrect.  Add a comment so I stop trying to "fix" this.

Change-Id: I377afaf373af5f6c09d76878d3ea43a48ac6b84a
Reviewed-on: https://chromium-review.googlesource.com/c/apps/libapps/+/2572037
Reviewed-by: Joel Hockey <9ecfc52dc2ffef73afac73f3495f294aeddf1231@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

chromium/hterm,chromium/hterm,chromium/hterm,chromium/hterm