Keep internal stack trace methods declaring classes live

We now store the declaring classes in the internal stack trace to
make sure class unloading doesn't unload any classes owning methods
in the stack trace.

This fixes DexClassLoaderTest in libcore. Added regression test.

Bug: 22720414

Change-Id: I185f87c8ec0807e83f4661bd5bb5652dba6fc281
4 files changed