Update LayoutTests to use '%23' instead of '#' in data URIs

This is a (very) partial reland of
https://chromium-review.googlesource.com/c/chromium/src/+/738395,
restoring only the changes to LayoutTests. This should be safe since
'%23' always has been a correct encoding of '#' and so should work with
the data URI code as it is today. It will also make any future re-land
of the core original CL easier.

Bug: 123004
Change-Id: I87126ea0e3fd39756e571a8e6cf966107e7f7209
Reviewed-on: https://chromium-review.googlesource.com/1048287
Reviewed-by: David Benjamin <davidben@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559130}
8 files changed