Simplify & optimize StringImpl::replace(UChar, UChar)

Simplify & optimize StringImpl::replace(UChar, UChar)

StringImpl::replace(UChar, UChar) is mentioned as one of the
hot spots by the Intel VTune Amplifier profile when running
the 'textarea-dom.html' performance test.

StringImpl::replace(UChar, UChar) is optimized (and simplified)
by using 'StringImpl::find' method instead of manual traversing
the internal buffer and checking 'is8Bit' property value on
each iteration.

This changes gives approx 2.25% improvement of the average
'textarea-dom.html' performance test results (linux desktop x64,
GCC 4.6.3, release content_shell build with enabled
'linux_dump_symbols' flag).

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175198

[Mikhail, 2014-05-30 14:09:31]

PTAL

[eseidel, 2014-05-30 17:30:22]

lgtm

Makes sense.

[commit-bot: I haz the power, 2014-05-30 17:32:10]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mikhail.pozdnyakov@intel.com/304273003/1

[commit-bot: I haz the power, 2014-05-30 18:56:15]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  blink_presubmit on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/blink_presubmit/builds/6538)

[commit-bot: I haz the power, 2014-05-30 19:38:25]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-05-30 19:38:25]

Try jobs failed on following builders:
  blink_presubmit on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/blink_presubmit/builds/6550)

[tkent, 2014-05-31 13:29:03]

The CQ bit was checked by tkent@chromium.org

[commit-bot: I haz the power, 2014-05-31 13:29:25]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mikhail.pozdnyakov@intel.com/304273003/1

[commit-bot: I haz the power, 2014-05-31 20:19:35]

Change committed as 175198