Implement SkBlurDrawLooper with SkLayerDrawLooper

This allows us to delete SkBlurDrawLooper (and leave only one draw
looper implementation).

BUG=skia:

Change-Id: I549af86b81babf19e3649bdffffe2fdb0b308d5a
Reviewed-on: https://skia-review.googlesource.com/10101
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
5 files changed