Non fatal errors on duplicated accessors

Non fatal errors on duplicated accessors.

BUG=https://code.google.com/p/dart/issues/detail?id=22019
R=johnniwinther@google.com

Committed: https://code.google.com/p/dart/source/detail?r=42767

[ahe, 2015-01-09 13:56:04]

Patchset #1 (id:1) has been deleted

[ahe, 2015-01-09 13:56:25]

ahe@google.com changed reviewers:
+ johnniwinther@google.com

[ahe, 2015-01-09 13:56:26]

Without the changes to class_members.dart, you get additional confusing errors
about invalid overrides:

tests/co19/src/Language/07_Classes/07_Classes_A07_t02.dart:17:11:
Error: Duplicate definition of 'f'.
Try to rename or remove this definition.
  int get f {return 1;}
          ^
tests/co19/src/Language/07_Classes/07_Classes_A07_t02.dart:16:8:
Info: Existing definition of 'f'.
  void f() {}
       ^
tests/co19/src/Language/07_Classes/07_Classes_A07_t02.dart:17:11:
Error: Getter 'f' in 'C' can't override method from 'C'.
  int get f {return 1;}
          ^
tests/co19/src/Language/07_Classes/07_Classes_A07_t02.dart:16:8:
Info: This is the method that cannot be overridden by a getter.
  void f() {}
       ^

[Johnni Winther, 2015-01-09 14:35:22]

lgtm

[ahe, 2015-01-12 10:15:37]

Committed patchset #2 (id:40001) manually as 42767 (presubmit successful).