Change the deferring delay in LayerFlush from a fixed value to a varying value

Change the deferring delay in LayerFlush from a fixed value to a varying value

[Title] Change the deferring delay in LayerFlush from a fixed value to a varying value
[Issue#] N/A
[Problem] In m.comic.naver.com, the contents are not shown quickly.
[Cause] Fixed 0.5s delay in LayerFlush reduces redundant tile repaints so that it
        can enhance a page loading time. However, it also causes a bad visual
        responsiveness because the view updates are deferred.
[Solution] The deferring delay is redesigned to gradually increase from 0 to 1.3
           seconds during page loading.

Change-Id: I7f7c687d18425d27d25a956661c2fbcd3beb66f1