Add some command line options to debug AST parsing of illegal dart

Add some command line options to debug AST parsing of illegal dart

There are 2 cmdline options added in this change
 1.  --source-from-ast  reprints out the source by walking whatever
AST was constructed from the parse.  This helps visualize what the
partially constructued AST looks like.
 2. --resolve-on-parse-errors this option has been availble to
API users, now it is exposed on the commandline.  

Used together, you can take dart source that doesn't parse and see
how well the static analyzer understand it.

Committed: https://code.google.com/p/dart/source/detail?r=6076

[scheglov, 2012-04-01 02:30:33]

LGTM