Roll external/skia 445b55736..cd25f6348 (1 commits)

https://skia.googlesource.com/skia.git/+log/445b55736..cd25f6348

2017-08-26 angle-deps-roller@chromium.org Roll skia/third_party/externals/angle2/ 511937d9a..ef6615170 (1 commit)

Test: Presubmit checks will test this change.
Change-Id: I74ed0ada0b33a4ef6bc29e6cbddc0b55a0ba1015