Convert most interfaces in dart:core to abstract classes.

lib/coreimpl/collections.dart

Index: lib/coreimpl/collections.dart
diff --git a/lib/coreimpl/collections.dart b/lib/coreimpl/collections.dart
index 7786d3d364f1457d4361282fb304d47ad4a1b4d3..67e74965b1b521b198f8d155fdb35536a777983e 100644
--- a/lib/coreimpl/collections.dart
+++ b/lib/coreimpl/collections.dart
@@ -138,7 +138,7 @@ class Collections {
         Maps._emitMap(o, result, visiting);
       }
     } else { // o is neither a collection nor a map
-      result.add(o == null ? 'null' : o);  // TODO(jjb): remove the null check
+      result.add(o.toString());

[ahe, 2012/09/18 12:30:56]

Shouldn't this just be:

result.add(o);

[Lasse Reichstein Nielsen, 2012/09/18 12:39:42]

Yeah. I don't like passing non-strings to StringBuffer, but I guess it's
currently allowed.

     }
   }