Add additional V8 performance tests (issue #960).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1292 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Improvements to v8::Persistent usage (issue #1001):
- Remove V8_USE_UNSAFE_HANDLES dependency.
- Don't create persistent handles for primitive types.
- Don't create persistent handles for stack traces.
- CefV8Value::IsObject() no longer returns true for Date types.
- Fix V8Test.ContextEntered test flakiness.

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1293 5089003a-bbd8-11dd-ad1f-f1f9622dbc98