Fix bug in proguard deobfuscation of file names.

Configure proguard to preserve stack traces in the test-dump so we can
properly test ahat's deobfuscation of stack traces.

Fix a bug in proguard deobfuscation of file names. Specifically, we
should always compute the file name based on the class associated with a
stack frame, regardless of whether or not the method has been
obfuscated.

Restructure test-dump program to test more cases of stack frame
deobfuscation.

Test: m ahat-test, with expanded proguard deobufscation test.
Change-Id: Idbb564147c6aea6b9c2091612ecf17c01070d5ac