Faster all the things!

 Bug: 5177959
 Improve browser startup. Elinate IO access on UI thread during startup
 by removing the super legacy ClearThumbnails task. Also rework how
 the hardware acceleration debug setting works to remove the requirement
 for initialized BrowserSettings in onCreate

Change-Id: I4c1014d380827af4833586e6a3ae842fd59aa48b
7 files changed