Add an Arguments::GetAll() function that returns all arguments as a
std::vector<v8::Local<v8::Value>>. This is more clear, concise, and
slightly more performant than the alternative of using
Arguments::GetRemaining() since it doesn't require trying to convert
and avoids unnecessary calls.

Add a test for the new method.

Reverted due to a compile error, now fixed.

BUG=None

Review-Url: https://codereview.chromium.org/2822373002
Cr-Commit-Position: refs/heads/master@{#465627}