Show tooltip with local variable value in Observatory debugger

- Add LocalVariableAnnotation to script-inset
- Tweak shortName for a closure
- Teach Script how to find local variable locations (not perfect yet)
- Send tokenPos and endTokenPos for debugger local variables

Performance improvements:
- Reduced script-inset update/computeAnnotations calls from 5 to 1 for each stack frame that is opened

R=rmacnak@google.com

Review URL: https://codereview.chromium.org//1126363005

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@45725 260f80e4-7a28-3924-810f-c04153c831b5
6 files changed