Bug 1611791 [wpt PR 21432] - Stop dispatching SMIL events while seeking, a=testonly

Bug 1611791 [wpt PR 21432] - Stop dispatching SMIL events while seeking, a=testonly

Automatic update from web-platform-tests
Stop dispatching SMIL events while seeking

Based on [1], 'beginEvent' and 'endEvent' should only be dispatched for
elements that are active at the seeked-to time and elements that were
active at the previous/old/seeked-from time but are inactive at the
seeked-to time (respectively). 'repeatEvent's should not be disaptched
while seeking.

To handle this, extend the TimingUpdate helper class with a map that
tracks what interval the active elements had before the seek operation,
and whether the timing update operation is a seek operation (called
"fast-forward" since we end up moving in the forward direction
regardless of the actual seek direction).
Apart from that, the dispatching of 'repeatEvent's are also inhibited,
as well as the notifications of repeats in general.

[1] https://www.w3.org/TR/SMIL3/smil-timing.html#q114

Bug: 1039886
Change-Id: I17d91b1355858ee0b916d4fa46b9572e685e40e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2020947
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#736289}

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wpt-commits: e03feecc468b65aadc66b24bf76dbd0d6acfff5b
wpt-pr: 21432