Feed seed_shader() iota through a context pointer.

As this array grows longer it causes troublesome code generation
when we're compiling offline, but it's easy as an argument.

Change-Id: I53526443f534f29d3bff17c3aec24a9e916c9b86
Reviewed-on: https://skia-review.googlesource.com/60564
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Herb Derby <herb@google.com>
10 files changed