Establish a global reference before saving a class into a global.

A local reference is obtained to the string class for the purpose of
using it later in another routine to create string object arrays.
However, the local reference is invalid by the time it is next used.
Making the string class reference a global reference eliminates the
problem.

Change-Id: I8a04642e0ed3060f2fff2cb63996559f004aacff