Mutation observers doesn't get notified of character data mutation made by the parser

[Ryosuke Niwa]

When MutationObserver is observing a text node e.g. via a subtree observation,
and the HTML parser appends more data to it, the observer never gets invoked
with mutation records of the character data mutation made by the parser.

<rdar://problem/42477645>

[Ryosuke Niwa]

Created attachment 355381 [details]
Fixes the bug

[Antti Koivisto]

Comment on attachment 355381 [details]
Fixes the bug

View in context: https://bugs.webkit.org/attachment.cgi?id=355381&action=review

> Source/WebCore/dom/CharacterData.cpp:102
> +    String oldData;
> +    if (UNLIKELY(mutationRecipients))
> +        oldData = m_data;

Maybe just set oldData unconditionally? It is not clear that a branch is faster than minor ref churn.

[Ryosuke Niwa]

(In reply to Antti Koivisto from comment #2)
> Comment on attachment 355381 [details]
> Fixes the bug
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=355381&action=review
> 
> > Source/WebCore/dom/CharacterData.cpp:102
> > +    String oldData;
> > +    if (UNLIKELY(mutationRecipients))
> > +        oldData = m_data;
> 
> Maybe just set oldData unconditionally? It is not clear that a branch is
> faster than minor ref churn.

Okay. I guess we'd catch it on perf bots if it regressed perf.

[Ryosuke Niwa]

Committed r238429: <https://trac.webkit.org/changeset/238429>

[Radar WebKit Bug Importer]

<rdar://problem/46204294>