1. Fixes for converting properties for fields:
1.1. Only if neither getter not setter are overridden. Note that we ignore the fact that it _might_ be overridden in some subclass that we don't see.
Without this assumption almost nothing can be a field.
2.2. Create final fields when possible.
2. Generate field formal parameters where possible.
R=brianwilkerson@google.com
BUG=
Review URL: https://codereview.chromium.org//109853003
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@31043 260f80e4-7a28-3924-810f-c04153c831b5
scheglov@google.com