Don't emit a resourcetiming entry for UACSS.
Resources from UA CSS should not be reported in resource timing. Data
URLs in general are not reported, as they have no initiator, but UACSS
images get an initiator type of "uacss" and incorrectly appear in the
performance timeline.
Bug: 333831248
Change-Id: I5f817d385254e06920346ab3e90a8c336108d90b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5749709
Reviewed-by: Hao Liu haoliuk@chromium.org
Reviewed-by: David Bokan bokan@chromium.org
Commit-Queue: Ian Clelland iclelland@chromium.org
Cr-Commit-Position: refs/heads/main@{#1341208}