Add deprecation message for kDataUriHasOctothorpe

We are aiming to deprecate this feature in M67. This warning may have
some false positives (as it is legal to use '#' as a fragment
identifier), but I have yet to find a case in the wild of someone
actually doing that.

Intent: https://groups.google.com/a/chromium.org/d/msg/blink-dev/_g_HnAHkMPo/1DrejG5mAgAJ

Bug: 123004
Change-Id: Ibace7288ddb6a814f51faec85c47a49b0d69a273
Reviewed-on: https://chromium-review.googlesource.com/888762
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Rick Byers <rbyers@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533298}
2 files changed