Compute the correct dst->src rect for bitmap tiles in SkGpuDevice

Compute the correct dst->src rect for bitmap tiles in SkGpuDevice

Use anisotropic scale to show bug in verylargebitmap test.

Cherry pick to M55

BUG=chromium:664615

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4774

Change-Id: If92eab6d26b9fb506670412a80df259f99db2a21
Reviewed-on: https://skia-review.googlesource.com/4774
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-on: https://skia-review.googlesource.com/4825
Reviewed-by: Brian Salomon <bsalomon@google.com>