Roll src/third_party/skia 6fb0b67:b6b0a6e
Roll src/third_party/skia 6fb0b67:b6b0a6e

Summary of changes available at:
https://chromium.googlesource.com/skia/+log/6fb0b67..b6b0a6e

CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
TBR=scroggo@google.com

Commits in this roll:
b6b0a6e bsalomon@google.com Remove rt flags that are not necessary
8cab9a7 joshualitt@chromium.org All batches do their own pipeline compare
e8d21e8 bsalomon@google.com Make readpixels work on GrTextures
dbe1e6f joshualitt@chromium.org Give GrBatch a pointer to GrPipeline
3e5f555 jvanverth@google.com Various GL testing fixes
c83a297 reed@google.com have canvas send discard instead of retain if the draw would overwrite everything
0df62e3 joshualitt@google.com Revert of Give GrBatch a pointer to GrPipeline (patchset #1 id:1 of https://codereview.chromium.org/1237283007/)
1170a12 joshualitt@chromium.org Give GrBatch a pointer to GrPipeline
5f7f428 caryclark@google.com increase gm offsetimagefilter stroke width
8a955af borenet@google.com Coverage script: fix missing data
767d273 mtklein@chromium.org Replace buggy_blend_modes GM with an exhaustive test.

Review URL: https://codereview.chromium.org/1235143006

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#339084}

ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend