Always pass v8::Isolate to v8::Number::New()

Always pass v8::Isolate to v8::Number::New() as this is now the preferred way
of constructing a Number:
https://code.google.com/p/v8/issues/detail?id=2487

R=haraken
BUG=

Review URL: https://chromiumcodereview.appspot.com/23799009

git-svn-id: svn://svn.chromium.org/blink/trunk@157550 bbb929c8-8fbe-4397-9dbb-9b2b20218538