Revert of Make SkPixelRef::isLocked() debug-only, remove related dead code. (patchset...

Revert of Make SkPixelRef::isLocked() debug-only, remove related dead code. (patchset #1 id:1 of https://codereview.chromium.org/940083002/)

Reason for revert:
Broke callers in chrome

../../skia/ext/platform_canvas_unittest.cc:421:56: error: no member named 'isLocked' in 'SkPixelRef'
  EXPECT_TRUE(platform_bitmap->GetBitmap().pixelRef()->isLocked());

Original issue's description:
> Make SkPixelRef::isLocked() debug-only, remove related dead code.
>
> DM's okay locally with no diffs, no failures.
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/8e65712486c66108677a9b0a55ad3e7ca94db555

TBR=reed@google.com,mtklein@google.com,mtklein@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/940323003