[Webkit-unassigned] [Bug 32846] New: Timeline Panel timings are polluted by DOM Mutation events (which force inline Style Recalculations)

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=32846

           Summary: Timeline Panel timings are polluted by DOM Mutation
                    events (which force inline Style Recalculations)
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: Mac OS X 10.5
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: Web Inspector
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: jaimeyap at google.com
                CC: timothy at hatcher.name, pfeldman at chromium.org,
                    jamesr at chromium.org


When inspecting a page, the InspectorController binds the DOMAgent, which from
my understanding registers DOM mutation event listener. This causes DOM
Mutation Events to fire for every DOM mutation (innerHTML parsing, dom node
appends, document fragment appends, etc...).

This gets compounded by the fact that whenever a JS event handler for a DOM
event is fired at a document context a call to
Document::updateStyleForAllDocuments() is made. Thus firing DOM Mutation events
repeatedly forces styles to be up to date inline with each mutation instead of
getting deferred.

see https://bugs.webkit.org/show_bug.cgi?id=32580 which is Jamesr's pending
attempt to address the inline recalculation of styles.

But a proper fix would be to somehow disable DOMMutation event dispatches when
the timeline agent is recording.

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