Cleanup mac specific TextLayout measurement helper

Cleanup mac specific TextLayout measurement helper

As far as my analysis goes the rebaselines are needed due to the different kerning behaviour. The textLayout based measurement returns kerned values when measuring substrings of a run. When not using textLayout, we create a new run and pass that to Font::width which then returns a value that is not kerned for only the last character in the run. The new behaviour is consistent with the behaviour on non-mac, thus I don't see an issue with changing this. Additionally,  RenderText::width and ::widthFromCache behave the same way, creating new runs for measurement.

BUG=329543
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=164915

[eae, 2014-01-09 16:57:06]

LGTM

[commit-bot: I haz the power, 2014-01-10 23:36:51]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dominik.rottsches@intel.com/110313003/...

[commit-bot: I haz the power, 2014-01-11 01:34:46]

Change committed as 164915

[Dominik Röttsches, 2014-01-14 13:29:35]

Nice, the perf dashboard seems to appreciate the change:

Delta	Revision Range	Bot	Test Suite	Test
129.4%	244366-244392	chromium-rel-mac6	blink_perf	Layout_ArabicLineLayout
100.0%	244426-244427	chromium-rel-mac8	blink_perf	Layout_ArabicLineLayout

https://chromeperf.appspot.com/report?masters=ChromiumPerf&bots=chromium-rel-...