Copy the GL2 extension string before destroying context

The pointer returned by glGetString is owned by the GL context, so
when the GL context is destroyed it may become invalid. This happens
on Mesa, for example. Make/manage our own copy of the extension string
to use after destroying the context.

Bug: 9627179
Change-Id: I605536151ee64f50403546d0d38c5b5f1f27dd73
1 file changed