Implement V8ValueTraits<T>::toV8Value conversion functions

Add toV8Value functions to V8ValueTraits<T>. It converts many types to v8::Handle<V8::Value>.
Make ScriptPromiseResolver and ScriptPromiseResolverWithContext use them.

BUG=352552
R=haraken

Review URL: https://codereview.chromium.org/238723009

git-svn-id: svn://svn.chromium.org/blink/trunk@171932 bbb929c8-8fbe-4397-9dbb-9b2b20218538