Revert 168224 - Update V8 to version 3.15.4.

Revert 168224 - Update V8 to version 3.15.4.

Caused failures in WebKit layout tests:

Regressions: Unexpected text-only failures (6)
  fast/dom/Window/replaceable.html [ Failure ]
  http/tests/security/cross-frame-access-object-prototype.html [ Failure ]
  inspector/console/command-line-api-inspect.html [ Failure ]
  inspector/console/console-format-collections.html [ Failure ]
  inspector/runtime/runtime-localStorage-getProperties.html [ Failure ]

Regressions: Unexpected crashes (1)
  inspector/console/console-dir.html [ Crash ]

BUG=

Review URL: https://chromiumcodereview.appspot.com/11419039

TBR=yangguo@chromium.org
Review URL: https://codereview.chromium.org/11411036

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@168240 0039d316-1c4b-4281-b951-d872f2087c98