Move SplayTreeMap from coreimpl to collection.

tests/html/indexeddb_2_test.dart

 #library('IndexedDB1Test');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
-#import('dart:coreimpl');
+#import('dart:collection');
 #import('utils.dart');
 
 // Write and re-read Maps: simple Maps; Maps with DAGs; Maps with cycles.
 
 const String DB_NAME = 'Test';
 const String STORE_NAME = 'TEST';
 const int VERSION = 1;
 
 testReadWrite(key, value, check,
               [dbName = DB_NAME,
@@ skipping 108 matching lines @@
   go('test_simple', obj1);
   go('test_DAG', obj2);
   go('test_cycle', obj3);
   go('test_simple_splay', obj4);
   go('const_array_1', const [const [1], const [2]]);
   go('const_array_dag', const [const [1], const [1]]);
   go('array_deferred_copy', [1,2,3, obj3, obj3, 6]);
   go('array_deferred_copy_2', [1,2,3, [4, 5, obj3], [obj3, 6]]);
   go('cyclic_list', cyclic_list);
 }