Cleanup WebNinePatchLayerImpl by removing setBitmap(SkBitmap, const WebRect&)

This is no longer needed as WebNinePatchLayer has removed this method.

TBR=jamesr@chromium.org

Review URL: https://codereview.chromium.org/595213002

Cr-Commit-Position: refs/heads/master@{#296394}
2 files changed