Add support for using ANGLE in bench_pictures.

BUG=https://code.google.com/p/skia/issues/detail?id=1012

Other cleanups:
Remove setDeviceType from PictureBenchmark, since it is unnecessary.
Dereference PictureRenderer::fGrContext when done with it.
Make PictureRenderer::fGrContext and PictureRenderer::fGrContextFactory private, since they are not used by subclasses.

Review URL: https://codereview.appspot.com/7314063

git-svn-id: http://skia.googlecode.com/svn/trunk@7677 2bbb7eff-a529-9590-31e7-b0007b416f81
5 files changed