Roll external/skia 38784599f..d85db6096 (5 commits)

https://skia.googlesource.com/skia.git/+log/38784599f..d85db6096

2018-05-31 djsollen@google.com Expose API for temporary use by the Android WebView.
2018-05-24 scroggo@google.com Alternate between two SkBitmaps in SkAnimatedImage
2018-05-24 scroggo@google.com Make DNG decodes single threaded on Android
2018-05-10 scroggo@google.com Cherry-pick "Fix extra texture creation in GrResourceProvider::createTexture() with SRGB data."
2018-05-10 scroggo@google.com Treat SkFILEStream's fOriginalOffset as the start

The AutoRoll server is located here: https://android-next-roll.skia.org

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
be CC'd on the roll, and stop the roller if necessary.

Test: atest CtsUiRenderingTestCases:.LayerTests
Bug: 79619253
Merged-In: Iea460fb2a9c7d84e88acc7d625a9f5c6135bc2e8
Change-Id: Id9a3466b6399b72d734da387f870ba7b98700021