We only need metric from top level content document, but we dont have
any information about it in nsDOMNavigationTiming, so I add a weak
reference which points to nsDocShell.
MozReview-Commit-ID: GiJigRLYHNV
This adds a probe called TIME_TO_NON_BLANK_PAINT_MS which reports time to
non-blank paint for root content documents whose docshell was active for the
entire time between navigation start and first non-blank paint.
MozReview-Commit-ID: 7JQdk5vHr1O
The testcase has an svg-as-image inside an svg-as-image. At shutdown the viewer of the inner svg-as-image is destroyed (via the shutdown observer) first. Then the outer svg-as-image destroys its viewer which tries to unregister all image requests from the refresh driver. So it unregisters the inner svg-as-image, which calls GetAnimated.
This patch gives ns{I,}Document the ability to track use counters and
also to send those to telemetry at document destruction time. We push
things to telemetry lazily because we're can't definitively say whether
something has been used until the document is torn down.
