[es6] Use SubString in String{Starts,Ends}With

[es6] Use SubString in String{Starts,Ends}With

Much faster and constant than always searching the whole string

````
var allCodePoints = [];
for (var i = 0; i < 65536; i++) allCodePoints[i] = i;
var allCharsString = String.fromCharCode.apply(String, allCodePoints);

function bench(search) {
  var counter = 0;
  print(search + " found at " + allCharsString.startsWith(search));
  var start = Date.now();
  while (counter++ < 5000000) {
    allCharsString.startsWith(search);
  }
  var end = Date.now();
  print(end - start);
  return counter;
}

print("single character");
bench("\u0000");
bench("\u0050");
bench("\u1000");
````

OLD

single character
 found at true
374
P found at false
559
က found at false
13492

NEW

single character
 found at true
261
P found at false
146
က found at false
146

BUG=v8:4384
LOG=N

Committed: https://crrev.com/d42920ce06853d2982f52a9023ad4652f09a9277
Cr-Commit-Position: refs/heads/master@{#30599}

[skomski, 2015-09-03 16:13:16]

karl@skomski.com changed reviewers:
+ littledan@chromium.org

[skomski, 2015-09-04 17:51:57]

karl@skomski.com changed reviewers:
+ jkummerow@chromium.org

[Dan Ehrenberg, 2015-09-04 18:17:24]

The CQ bit was checked by littledan@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-04 18:17:33]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1321853006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1321853006/1

[Dan Ehrenberg, 2015-09-04 18:18:41]

lgtm

[commit-bot: I haz the power, 2015-09-04 18:20:35]

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

[commit-bot: I haz the power, 2015-09-04 18:20:36]

Dry run: Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/5566)

[Dan Ehrenberg, 2015-09-04 18:27:11]

On 2015/09/04 at 18:20:36, commit-bot wrote:
> Dry run: Try jobs failed on following builders:
>   v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/5566)

** Presubmit Warnings **
karl@skomski.com is not in AUTHORS file. If you are a new contributor, please
visit
http://www.chromium.org/developers/contributing-code and read the "Legal"
section
If you are a chromite, verify the contributor signed the CLA.

[Dan Ehrenberg, 2015-09-04 18:29:08]

On 2015/09/04 at 18:27:11, Dan Ehrenberg wrote:
> On 2015/09/04 at 18:20:36, commit-bot wrote:
> > Dry run: Try jobs failed on following builders:
> >   v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/5566)
> 
> ** Presubmit Warnings **
> karl@skomski.com is not in AUTHORS file. If you are a new contributor, please
visit
> http://www.chromium.org/developers/contributing-code and read the "Legal"
section
> If you are a chromite, verify the contributor signed the CLA.

There does seem to be a CLA in place for you. I am not sure what problem the
infrastructure is having.

[Jakob Kummerow, 2015-09-04 18:37:53]

ACK. However, note that creating a substring causes an allocation, which isn't
100% ideal either. That said, incremental improvement is fine, and if we want
even more speed in the future we can always think about further optimizations
(like implementing substring comparisons in the compilers, or exposing the C++
string-search implementation to JS builtins, or something).

The AUTHORS entry will land in https://codereview.chromium.org/1324453007/.

[skomski, 2015-09-04 18:39:51]

On 2015/09/04 18:29:08, Dan Ehrenberg wrote:
> On 2015/09/04 at 18:27:11, Dan Ehrenberg wrote:
> > On 2015/09/04 at 18:20:36, commit-bot wrote:
> > > Dry run: Try jobs failed on following builders:
> > >   v8_presubmit on tryserver.v8 (JOB_FAILED,
> http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/5566)
> > 
> > ** Presubmit Warnings **
> > mailto:karl@skomski.com is not in AUTHORS file. If you are a new
contributor, please
> visit
> > http://www.chromium.org/developers/contributing-code and read the "Legal"
> section
> > If you are a chromite, verify the contributor signed the CLA.
> 
> There does seem to be a CLA in place for you. I am not sure what problem the
> infrastructure is having.

I need to add myself to AUTHORS since my other commit was reverted.

[skomski, 2015-09-04 21:21:50]

The CQ bit was checked by karl@skomski.com

[commit-bot: I haz the power, 2015-09-04 21:22:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1321853006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1321853006/1

[commit-bot: I haz the power, 2015-09-04 21:24:36]

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

[commit-bot: I haz the power, 2015-09-04 21:24:36]

Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/5573)

[skomski, 2015-09-04 21:32:44]

The CQ bit was checked by karl@skomski.com

[commit-bot: I haz the power, 2015-09-04 21:32:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1321853006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1321853006/1

[commit-bot: I haz the power, 2015-09-04 21:34:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-04 21:34:48]

Patchset 1 (id:??) landed as
https://crrev.com/d42920ce06853d2982f52a9023ad4652f09a9277
Cr-Commit-Position: refs/heads/master@{#30599}