chromeos: makes changes to can activate go to server

This is necessary as it's not uncommon to have code like this:

  SetCanActivate(true);
  widget->Activate();
  SetCanActivate(false);

BUG=928939
TEST=none

Change-Id: I52c2d79cd7aec2fe5ab13f8ae7821227f1a0214e
Reviewed-on: https://chromium-review.googlesource.com/c/1457117


Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629866}