Update active style in InspectorCSSAgent::MatchingStyles

MatchingStyles can apparently be called from from within probe::
AnimationPlayStateChanged. Updating style synchronously here means
that new animations can start (via CSS animations). The animations team
wants to prohibit starting/updating animations from within the probe
call (see bug for details). Therefore we must avoid recalculating
style here, since that _may_ trigger new/updated animations.

As it happens, we don't actually need to recalculate the style, since
this function is only matching selectors. It's sufficient to
UpdateActiveStyle() instead, which ensures that information needed for
selector matching is up-to-date.

Fixed: 1106539
Change-Id: I75eb10ee1792f78ca1e5d44e42a63974af55162a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2317795Reviewed-by: Alex Rudenko <alexrudenko@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792213}

third_party/blink/renderer/core/inspector/inspector_css_agent.cc

@@ -2326,7 +2326,7 @@ HeapVector<Member<CSSStyleDeclaration>> InspectorCSSAgent::MatchingStyles(
   // This ensures that active stylesheets are up-to-date, such that
   // the subsequent collection of matching rules actually match against
   // the correct RuleSets.
-  element->GetDocument().UpdateStyleAndLayoutTreeForNode(element);
+  element->GetDocument().GetStyleEngine().UpdateActiveStyle();
 
   HeapVector<Member<CSSStyleRule>> rules =
       FilterDuplicateRules(style_resolver.PseudoCSSRulesForElement(