The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5b334c2c1dd5c2516fc71a66550b65b982b67d5c

commit 5b334c2c1dd5c2516fc71a66550b65b982b67d5c
Author: Yuwei Huang <yuweih@chromium.org>
Date: Fri Aug 11 00:44:04 2017

[CRD iOS] Fix jarring show keyboard UX

Currently when the user taps Show Keyboard, the host view will flicker
and the aspect ratio will appear to be wrong in a short time. The
problem could be that we needed to change the OpenGL viewport size and
the viewport constraints at the same time (to adjust for the size of
the soft keyboard), but in reality they are done in different threads,
causing intermediate out-of-sync.

This CL avoids the need to change the OpenGL viewport by simply not
changing the size of the host view -- we still move the FAB icon up and
update the viewport constraint to prevent the desktop from going under
the keyboard, but we keep the host view always stretched to the whole
screen and just let the keyboard cover the black area below the desktop
image.

Bug:  753620 
Change-Id: I1436d5166ac6296e0df895a58cb960d5aa711f00
Reviewed-on: https://chromium-review.googlesource.com/607100
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493622}
[modify] https://crrev.com/5b334c2c1dd5c2516fc71a66550b65b982b67d5c/remoting/ios/app/host_view_controller.mm
[modify] https://crrev.com/5b334c2c1dd5c2516fc71a66550b65b982b67d5c/remoting/ios/session/remoting_client.h
[modify] https://crrev.com/5b334c2c1dd5c2516fc71a66550b65b982b67d5c/remoting/ios/session/remoting_client.mm

Verified fixed in 63.0.3220.0