Use a UniquePtr to clean up global logging std::string*s.

This makes valgrind happier.
Bug: 11670287

Change-Id: I957b94cdc177665e66b069e4d2b2b8d0a4b589c8

Conflicts:
	runtime/base/logging.cc
Avoid unnecessary copy of dex_gc_map.

Change-Id: I8a7209d92aeee853f6a4e9e9bb0e094c5acd5e05
Avoid some string allocations.

Also avoid building a string one character at a time.

Change-Id: I3db26226c620a730b95637d5bfc23e2d4715cfb9

Conflicts:
	runtime/dex_file.cc