Revert 156783 "Refactoring DrawLooper so that it can apply shado..."

Reason for revert: unacceptable performance regressions
TBR=vmpstr

> Refactoring DrawLooper so that it can apply shadow effects as skia image filters
> 
> This fixes a bug where a bitmap's alpha channel was not being blurred when
> rendering 2D canvas shadows.
> 
> BUG=100703
> R=senorblanco
> TEST=LayoutTest fast/canvas/canvas-drawImage-shadow-blur.html
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=156733
> 
> Review URL: https://chromiumcodereview.appspot.com/23102018

TBR=junov@chromium.org

Review URL: https://codereview.chromium.org/23461012

git-svn-id: svn://svn.chromium.org/blink/trunk@156865 bbb929c8-8fbe-4397-9dbb-9b2b20218538