Roll src/third_party/skia bf15b6676843..d51d00745b1d (6 commits) (#8584)

https://skia.googlesource.com/skia.git/%2Blog/bf15b6676843..d51d00745b1d

git log bf15b6676843625cf68b9df44705d808cf8236c7..d51d00745b1ddad78b777973c9df56d351ff5e02 --date=short --no-merges --format=%ad %ae %s
2019-04-15 mtklein@google.com add _M_ARM64 support
2019-04-15 csmartdalton@google.com Support multisample in GrProxyProvider::MakeFullyLazyProxy
2019-04-15 mtklein@google.com add retries to fm_bot
2019-04-15 jvanverth@google.com Fix fontcache GMs on Metal.
2019-04-15 reed@google.com use slope-guess for faster charToGlyph
2019-04-11 herb@google.com Reland "Convert the CPU mask case to use prepareForDrawing"

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': 'bf15b6676843625cf68b9df44705d808cf8236c7',
+  'skia_revision': 'd51d00745b1ddad78b777973c9df56d351ff5e02',
 
   # 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: c3dc0e107b8c4e016760548925328356
+Signature: c15d1d88a20c0b676e6b7fe141f0272a
 
 UNUSED LICENSES: