Roll external/skia ef4047db9..2d4f7cbdc (14 commits)

https://skia.googlesource.com/skia.git/+log/ef4047db9..2d4f7cbdc

2018-11-28 herb@google.com Move the empty glyph checks into the common code
2018-11-28 kjlubick@google.com [canvaskit] Fix arc() call
2018-11-28 kjlubick@google.com gn format gn/opts.gni
2018-11-28 michaelludwig@google.com Reland "Initial definition of fill rect op"
2018-11-28 herb@google.com Fix up GrGlyphCache ctor
2018-11-28 reed@google.com remove legacy hinting-enum guards
2018-11-28 michaelludwig@google.com Revert "Initial definition of fill rect op"
2018-11-28 scroggo@google.com Build Android Framework host library on Mac
2018-11-28 michaelludwig@google.com Initial definition of fill rect op
2018-11-28 kjlubick@google.com [canvaskit] support globalAlpha and dashed strokes
2018-11-28 bsalomon@google.com Remove SkCanvas::ImageSetEntry constructors
2018-11-28 herb@google.com Remove unneeded inline declarations
2018-11-28 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/swiftshader 3b003a51bc9a..79d0e565b001 (1 commits)
2018-11-28 borenet@google.com [infra] Flutter bot should sync to origin/skia-master

The AutoRoll server is located here: https://autoroll-internal.skia.org/r/android-master-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, who should
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Test: Presubmit checks will test this change.
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Test: lunch sdk && mmma external/skia on Mac
Bug: 118742766
Change-Id: Ib7e0e8cd0c451b8b31a14f5efa3cd9649336d973