Introduce skia_pic gyp variable.

skia_pic tells ninja to use -fPIC when building for position
independent code.

Set skia_pic to true when building our existing targets that
require position independent code.

Also use skia_pic when building for Android.

R=mtklein@google.com, djsollen@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/406613003
2 files changed