Revert 133468 - Fix wallpaper fade animation flashing problem.

Revert 133468 - Fix wallpaper fade animation flashing problem.


This CL fix the wallpaper fade animation problem. The problem was when user
switched to a new wallpaper, it seems there is a white flashing before new
wallpaper fade in.
The reason was I started the hide animation before loading new wallpaper. And it
took around 300ms to load while the animation finished around 200ms. So there is
100ms period where the background color (white) showed up.
I delayed the hide animation, but then another problem showed up. Now the show
and hide animation happened at the same time. At some point in the animation,
the background color will have 25% opacity and it also cause a flashing.

To fix all, this CL only animate on Show new wallpaper and delete the old widget
after the Show animation completed.

BUG=118651
TEST=Change wallpaper in chromeos, and verify if the animation is smooth.

Review URL: http://codereview.chromium.org/10146016

TBR=bshe@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=133514