Roll src/third_party/skia e4628b10722f..51874e3e3712 (2 commits) (#8445)

https://skia.googlesource.com/skia.git/%2Blog/e4628b10722f..51874e3e3712

git log e4628b10722f09adfb49943a43b9668fb9a02723..51874e3e371230e2cc02912ed0c9ddb569e48532 --date=short --no-merges --format=%ad %ae %s
2019-04-04 bungeman@google.com Allow selection of shaper wrapping algorithm.
2019-04-04 halcanary@google.com SkPDF: Use fewer complex PathOps to speed up clipping

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 (jlavrova@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': 'e4628b10722f09adfb49943a43b9668fb9a02723',
+  'skia_revision': '51874e3e371230e2cc02912ed0c9ddb569e48532',
 
   # 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: 80674cf6dbe928ef708c6790cf83b6bd
+Signature: 71fc8d0d1ecce72de33ca2aa449ab4a7
 
 UNUSED LICENSES: