Roll src/third_party/skia 1875353110d1..bf15b6676843 (8 commits) (#8582)

https://skia.googlesource.com/skia.git/%2Blog/1875353110d1..bf15b6676843

git log 1875353110d12bda6374d099a159937fad48de72..bf15b6676843625cf68b9df44705d808cf8236c7 --date=short --no-merges --format=%ad %ae %s
2019-04-15 mtklein@google.com dump stack trace in FM on failure
2019-04-15 scroggo@google.com Implement SkHeifCodec::onRewind
2019-04-15 mtklein@google.com restore vmull_u8() in color32()
2019-04-15 brianosman@google.com Guard GrRadialGradientLayout::TestCreate against Empty shaders
2019-04-15 fmalita@chromium.org [skottie] 'Add' layer blend mode support
2019-04-13 mtklein@google.com step carefully in decal_nofilter_scale
2019-04-15 skia-autoroll@skia-public.iam.gserviceaccount.com Roll skia/third_party/skcms 0da672fc2c69..668026c511f3 (1 commits)
2019-04-12 mtklein@google.com always zero SkMallocPixelRefs

The AutoRoll server is located here: https://autoroll.skia.org/r/skia-flutter-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff (herb@google.com), and stop
the roller if necessary.

DEPS

@@ -23,7 +23,7 @@ vars = {
   'fuchsia_git': 'https://fuchsia.googlesource.com',
   'github_git': 'https://github.com',
   'skia_git': 'https://skia.googlesource.com',
-  'skia_revision': '1875353110d12bda6374d099a159937fad48de72',
+  'skia_revision': 'bf15b6676843625cf68b9df44705d808cf8236c7',
 
   # When updating the Dart revision, ensure that all entries that are
   # dependencies of Dart are also updated to match the entries in the

ci/licenses_golden/licenses_skia

-Signature: 2b75b64230cb03a20539d4bcf9269748
+Signature: c3dc0e107b8c4e016760548925328356
 
 UNUSED LICENSES: