Speed up case folding for 8-bit strings

Speed up case folding for 8-bit strings

From http://trac.webkit.org/changeset/160954 by Anders Carlsson  <andersca@apple.com>;

"Add a case folding lookup table for 8-bit strings and use it instead of calling down to u_foldCase.
On a simple microbenchmark using a lookup table is about 15x faster."

The Intel Vtune Amplifier profiler showed 'ucase_fold()' calls among the top hotspots by CPU usage when profile the 'modify-element-classname.html' performance test and these calls were from 'WTF::equalIgnoringCase(const LChar* a, const LChar* b, unsigned length)'.

This patch optimizes 'WTF::equalIgnoringCase()' so that the test's median time value falls approximately by 12% and the profiler shows the following delta of the total CPU time for the whole test execution: 3.550s - 3.145s = 0.405s

Considering that 'WTF::equalIgnoringCase()' is a generic function and it is used very intensively in many places we can anticipate significant performance improvements for other scenarios as well.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196478

[Mikhail, 2015-06-03 13:13:24]

mikhail.pozdnyakov@intel.com changed reviewers:
+ tkent@chromium.org

[Mikhail, 2015-06-03 13:19:28]

mikhail.pozdnyakov@intel.com changed reviewers:
+ thakis@chromium.org

[Mikhail, 2015-06-03 13:21:15]

PTAL

[tkent, 2015-06-04 02:05:20]

Please add a unit test to verify that the fast path and the slow path produce
same results.

[Mikhail, 2015-06-04 06:56:31]

On 2015/06/04 02:05:20, tkent wrote:
> Please add a unit test to verify that the fast path and the slow path produce
> same results.

done

[tkent, 2015-06-04 06:58:54]

The CQ bit was checked by tkent@chromium.org

[tkent, 2015-06-04 06:58:55]

lgtm

[commit-bot: I haz the power, 2015-06-04 06:59:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1152163005/20001

[commit-bot: I haz the power, 2015-06-04 08:06:11]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196478