Ignore draw requests when the display is off

When WindowManagerService's events are enabled/disabled, the state of the
display is dispatched to the known windows. This allows ViewRootImpl to
ignore draw requests until the screen is turned back on. This can potentially
lead to significant battery savings. For instance, a launcher widget showing
a repeating animation will cause the CPU and the GPU to wake up regularly
without this change.
(Change submitted by Intel and merged manually)

Change-Id: I7f93b0e60c3e6de1705f619e80860c36b1cdb978