Add SaveLayer-Draw-Restore optimization.

Add SaveLayer-Draw-Restore optimization.

This is like SkPictureRecord's remove_save_layer1 but works with all draw calls.

Interesting patterns removed:
  SaveLayer-DrawRect-Restore: Silk SKPs, desk_weather
  SaveLayer-DrawPath-Restore: desk_carsvg, desk_wowwiki, tabl_androidpolice
  SaveLayer-DrawPosTextH-Restore: tabl_android_police
There may be others, but I stopped looking.

BUG=skia:2378
R=robertphillips@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/269813010

git-svn-id: http://skia.googlecode.com/svn/trunk@14610 2bbb7eff-a529-9590-31e7-b0007b416f81