Gif frames continue even if the webkit changes aren't drawn.
When we suspend drawing, suspend the gif animation as well.
This is accomplished by fooling webkit into thinking the
browser window is offscreen. When the webkit drawing is
resumed, invalidate the entire content so the gif animations
start up once more.
requires companion change in external/webkit
http://b/2621902
Change-Id: I1814aa41630820872d62752b75ae94383fdcc5fc
75796bbef7