Roll external/skia 1eace2db4..1af03d439 (3 commits)

https://skia.googlesource.com/skia.git/+log/1eace2db4..1af03d439

2017-07-31 jvanverth@google.com Compute correct bounds for DrawShadowRec.
2017-07-31 ethannicholas@google.com updated spirv-tools to latest version
2017-07-31 bsalomon@google.com Don't create GrAtlasTextBlobs for zero glyph count text draws.

Test: Presubmit checks will test this change.
Change-Id: Ief3ed7a97d143f5078d0b7c07537dfce08ae8bcf