Roll external/skia c34676349..d67e51898 (10 commits)

https://skia.googlesource.com/skia.git/+log/c34676349..d67e51898

2017-12-11 brianosman@google.com Move ImGui support code to ImGuiLayer
2017-12-11 csmartdalton@google.com CCPR: Don't use instanced draw calls with geometry shaders
2017-12-11 halcanary@google.com apps/build.gradle: skiaOut is now absolute since a2e7f5ae10
2017-12-11 fmalita@chromium.org Fix SampleLua build
2017-12-11 brianosman@google.com Create a Window::Layer interface to reduce sk_app glue code
2017-12-11 mtklein@chromium.org The downsamplebitmap_image GMs only use one image.
2017-12-11 mtklein@chromium.org Revert "add experimental bilerp_clamp_8888 stage"
2017-12-11 benjaminwagner@google.com Add Goma Test/Perf jobs.
2017-12-11 halcanary@google.com resources: file moved
2017-12-11 mtklein@chromium.org add experimental bilerp_clamp_8888 stage

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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: I4ea50c7a333bca6c10c0a99bd6c09a878dfd93f7
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