[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

Review URL: https://codereview.chromium.org/1321853006

Cr-Commit-Position: refs/heads/master@{#30599}
1 file changed
tree: 26c3f7c4dedc0ad097d74e7c13b8a593e2baa3c3
  1. benchmarks/
  2. build/
  3. include/
  4. infra/
  5. samples/
  6. src/
  7. test/
  8. testing/
  9. third_party/
  10. tools/
  11. .clang-format
  12. .gitignore
  13. .ycm_extra_conf.py
  14. AUTHORS
  15. BUILD.gn
  16. ChangeLog
  17. codereview.settings
  18. DEPS
  19. LICENSE
  20. LICENSE.strongtalk
  21. LICENSE.v8
  22. LICENSE.valgrind
  23. Makefile
  24. Makefile.android
  25. Makefile.nacl
  26. OWNERS
  27. PRESUBMIT.py
  28. README.md
  29. WATCHLISTS
README.md

V8 JavaScript Engine

V8 is Google's open source JavaScript engine.

V8 implements ECMAScript as specified in ECMA-262.

V8 is written in C++ and is used in Google Chrome, the open source browser from Google.

V8 can run standalone, or can be embedded into any C++ application.

V8 Project page: https://code.google.com/p/v8/

Getting the Code

Checkout depot tools, and run

    fetch v8

This will checkout V8 into the directory v8 and fetch all of its dependencies. To stay up to date, run

    git pull origin
    gclient sync

For fetching all branches, add the following into your remote configuration in .git/config:

    fetch = +refs/branch-heads/*:refs/remotes/branch-heads/*
    fetch = +refs/tags/*:refs/tags/*