The Charge Splash screen (go/cros-charging-splash) requires showing
the battery charge splash screen until either the user presses the
power button or a timeout is hit and the device shuts back down. In
order to continue showing the splash screen, frecon needs to retain DRM
master, rather than giving it to Chrome to show the login screen.
However, once the user presses the power button, the login screen needs
to be shown, which requires frecon dynanmically giving DRM master to
Chrome when required.

To support conditionally giving DRM master, add the |--wait-drop-master|
option. When this option is used, frecon will not drop DRM master for
Chrome to take over until it's told to. Additionally, add the escape
code |drmdropmaster| to inform frecon to drop DRM master, so Chrome can
take it over.

BUG=b:228370390
TEST=Manual verification: Boot Skyrim DUT

Change-Id: I6f1863171934725566e9478347ce1860ac29df9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/frecon/+/4491364


Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Dominik Behr <dbehr@chromium.org>
Tested-by: Tim Van Patten <timvp@google.com>