Upgrade cglib to 3.1, fix ASM5 breakages

This now passes internal Google tests.
I had to upgrade cglib to 3.1 to fix JUnit breakages
that are triggered by ASM 5. I also had to revert the
DevMode 'JavaScriptHost.checkNotNull' change which was
never merged into the Google branch.

Change-Id: Ic41d597fc91179f610705884aeb64f5de8f72b13