GrGradientEffect::onIsEqual() must also consider tiling

Without this fix, the newly added GM draws incorrectly.

Change-Id: Ic159ab3201c10369ad5f8151186245d8d076cc25
Reviewed-on: https://skia-review.googlesource.com/30484
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
2 files changed