freezer: disable on "am dumpheap <pid>"

heapDump() is used to collect process heaps via "am dumpheap <pid>". It is
alternative to "dumpsys meminfo" and would hang if called on a frozen
process. In this patch:

 - disable freezer before the binder transaction to collect heap data
 - install a man-in-the-middle callback to handle completion of
   collection. The new callback will invoke the original one from the client
   and then enable the freezer again.

Change-Id: I43f501a88a7325d1bd2b3d1c6eb4a4d03b97a691
Test: am dumpheap <frozen process pid>
Bug: 151225245