JPEG YUV Decoding

Enabling JPEG YUV Decoding in Skia

BUG=skia:3005, skia:1674, skia:3029

Committed: https://skia.googlesource.com/skia/+/8e6c3b93a39e19111662a760ede97df55e51d39f

Review URL: https://codereview.chromium.org/399683007
Remove AutoScratchTexture

Remove AST from GrClipMaskCache

Remove AST from GrClipMaskManager

BUG=skia:2889

R=robertphillips@google.com

Review URL: https://codereview.chromium.org/663583002
"Fix" debugger's setMatrix handling

This remedies two problems with the debugger's matrix handling:
1) the user matrix was not being passed to the setMatrix command (for a concat)
2) the setting of the user matrix was not consistently forcing a complete re-rendering of the scene

BUG=skia:3018

Review URL: https://codereview.chromium.org/660883002