Add @SafeVarargs for methods using typevar varargs.

Bug 27142336
Using a type variable in a varargs leads to a javac warning
because type variables are treated as Object after compilation.
Because these uses do not require a specific typed array, we
can use @SafeVarargs to suppress the warning.

Change-Id: I860bcc79667a9c85c381c7994fd1d798209d7c66