Stop supporting CSP-Report-Only in meta elements
Report-Only mode isn't allowed in <meta> elements per CSP 1.1, and
neither Firefox nor Edge supports it. This CL drops support and updates
layout tests that were relying on it.
BUG=
600513
Committed:
https://crrev.com/9f6871d833bca118dfa14d2888afb55e390a90e1
Cr-Commit-Position: refs/heads/master@{#385419}