Some refactoring for asan_symbolize.py: introduced the Symbolizer class and...

Some refactoring for asan_symbolize.py: introduced the Symbolizer class and implemented DarwinSymbolizer for atos-based symbolization, BreakpadSymbolizer for breakpad-based symbolization (files produced by the dump_syms tool, http://code.google.com/p/google-breakpad/source/browse/#svn%2Ftrunk%2Fsrc%2Ftools%2Fmac%2Fdump_syms) and ChainSymbolizer to allow falling back if a symbolizer hadn't succeeded.
Fixed pylint warnings.

llvm-svn: 161176