Remove children of title element before setting new title

Remove children of title element before setting new title

http://www.whatwg.org/specs/web-apps/current-work/multipage/dom.html#document.title

When setting the document title through the document.title or
<title>.text there was an optimization that reused a child text node
in the cases it could. But according to the specification, all
children must be removed and re-created with the new value.

Removing the optimization has a performance impact and makes setting
document.title (or <title>.text) up to ten times slower. This has been
deemed acceptable since the change should only be visible in
specialized micro-benchmarks. It is more important to align with other
browsers and the spec that don't do this optimization.

blink-dev thread about the performance regression:

https://groups.google.com/a/chromium.org/d/msg/blink-dev/ONBQQ5uhBik/fEiTrzQeYlkJ

This is a reland of:

https://codereview.chromium.org/128603002
https://codereview.chromium.org/107513013

The original WebKit bug:

https://bugs.webkit.org/show_bug.cgi?id=28864

BUG=330140, 331076
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=165309

[davve, 2014-01-16 09:59:56]

The actual code changes come verbatim from reverting the revert:

git revert -n 997e0f0046046f7303fb14a51660c1d2f280e293

I've updated the description with some conclusions from the blink-dev thread and
the link to the root message.

I've added you morrita as reviewer since you were involved in the blink-dev
thread. Do you think you can review it?

[davve, 2014-01-17 08:34:57]

Jochen, you have reviewed this before, do you mind taking a look now that this
has been through blink-dev. Sorry for the back-and-forth.

[jochen (gone - plz use gerrit), 2014-01-17 12:28:52]

rslgtm

[commit-bot: I haz the power, 2014-01-17 12:32:27]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/davve@opera.com/139313009/1

[commit-bot: I haz the power, 2014-01-17 13:40:23]

Change committed as 165309