Do not synchronously measure SVG text every time it changes

[vitorroriz]

97f84b2

Do not synchronously measure SVG text every time it changes
https://bugs.webkit.org/show_bug.cgi?id=264669
rdar://problem/118451741

Reviewed by Simon Fraser.

This is a optimization done in the Blink fork https://chromium.googlesource.com/chromium/src.git/+/34c351416a102e4ee510badb86fbc4f57604ccd0 and found by Ahmad Saleem.

If SVG text is set multiple times in a row, we would
measure text synchronously for every set, even though just the last
measurement would count. This patch marks it as "need layout", so
we measure text in the next layout.

* Source/WebCore/rendering/svg/RenderSVGText.cpp:
(WebCore::RenderSVGText::subtreeTextDidChange):

Canonical link: https://commits.webkit.org/271678@main

883a96f

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv-sim
✅ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash 883a96f)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv-sim
✅ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[Ahmad-S792]

@vitorroriz - does it show any performance improvement in WebKit through A/B Test or on any specific benchmark?

[vitorroriz]

@Ahmad-S792

@vitorroriz - does it show any performance improvement in WebKit through A/B Test or on any specific benchmark?

I don't know yet. I've tried running benchmarks for it before but I was having some build issues. I'm trying again now.

[vitorroriz]

A/B tests show no progression/regression for this patch. But since it is a bit specific (multiple consecutive updates of SVG text), it might be our benchmarks don't cover that and that's still a valid patch. Maybe @shallawa can have a look at it.

[webkit-commit-queue]

Committed 271678@main (97f84b2): https://commits.webkit.org/271678@main

Reviewed commits have been landed. Closing PR #21278 and removing active labels.

[shallawa]

What is so special about subtreeTextDidChange()? The same function buildLayoutAttributesForTextRenderer() is called from subtreeChildWasAdded() and subtreeChildWasRemoved() in the same file. So why do not we apply the same fix in these two functions as well?

Also are we sure this will not affect JS querying the SVG text in the same update-the-rendering this function is called?