Allow dumpstate to signal keystore to dump its stack

This is needed to debug hangs in keystore2.

Restricted to debuggable builds for now.

Bug: 186879912
Test: 'adb bugreport', then find the stack traces for keystore2 in the
      "VM TRACES JUST NOW" section of the main bugreport file.
Change-Id: I4434cab7e79cb4aae8bbb2e3a8abff02e0073c13
1 file changed