Revert of cc: Don't consider tiles at the layers raster_contents_scale incomplete...

Revert of cc: Don't consider tiles at the layers raster_contents_scale incomplete (patchset #3 of https://codereview.chromium.org/484363003/)

Reason for revert:
Unit test added fails all the time.

http://build.chromium.org/p/chromium.memory/builders/Linux%20ASan%20LSan%20Tests%20%283%29/builds/6770

Original issue's description:
> cc: Don't consider tiles at the layers raster_contents_scale incomplete
>
> When PictureLayerImpl chooses a scale to raster at, we should accept
> tiles at that scale as complete, and not try wait for tiles at some
> other scale to be filled in. Such a tiling may not even exist.
>
> R=enne, vmpstr
> BUG=406433
>
> Committed: https://chromium.googlesource.com/chromium/src/+/60c7d86bb7685d8ca04ee53ae20fcdd6cd37eb5f

TBR=enne@chromium.org,vmpstr@chromium.org,danakj@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=406433

Review URL: https://codereview.chromium.org/505723002

Cr-Commit-Position: refs/heads/master@{#291653}