Roll external/skia 74f623d16..82a62d2d4 (7 commits)

https://skia.googlesource.com/skia.git/+log/74f623d16..82a62d2d4

2017-11-07 ethannicholas@google.com Revert "refactored SkSLVarDeclaration out of existence"
2017-11-07 brianosman@google.com Test SkColorSpaceXformCanvas on GTX1070 bots
2017-11-07 ethannicholas@google.com refactored SkSLVarDeclaration out of existence
2017-11-07 liyuqian@google.com Update chromium codebase during add_legacy_flag.py
2017-11-07 kjlubick@google.com Restore Pixelbook jobs
2017-11-07 angle-deps-roller@chromium.org Roll skia/third_party/externals/angle2/ 5b09d90d9..bd3cd506f (1 commit)
2017-11-07 mtklein@chromium.org add DM::FontMgr to ok

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https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

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Test: Presubmit checks will test this change.
Change-Id: I32d33474803b4d95fc47ef1581bae98502510829
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