Show Desktop: break state with activation (only)

... not them becoming visible.
Latter doesn't work for most cases (unminimizing)
for obvious reasons (they're not minimized) and
when a new window is mapped, the focus stealing
prevention seems a good filter
(if it's not good enough to gain the focus,
it's not good enough to break the state either)

REVIEW: 123783
CCBUG: 346837
CCBUG: 346933
CCBUG: 347212