Merge third_party/skia/gyp from https://chromium.googlesource.com/a/external/skia/gyp.git at 21e2d90077b889f17dd1ca74b3cb6f76aa8b1a87

This commit was generated by merge_from_chromium.py.

Change-Id: Ib74a51559d43fa36e2d96babb69fe4cb3653e71d