Properly process dart:core classes if dart:core is imported with prefix.

lib/compiler/implementation/dart_backend/backend.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 const bool REMOVE_ASSERTS = false;
 
 class ElementAst {
   final Node ast;
   final TreeElements treeElements;
 
@@ skipping 209 matching lines @@
           ClassElement classElement = element;
           for (final member in classElement.localMembers) {
             final name = member.name.slowToString();
             // Skip operator names.
             if (name.startsWith(@'operator$')) continue;
             // Fetch name of named constructors and factories if any,
             // otherwise store regular name.
             // TODO(antonm): better way to analyze the name.
             fixedMemberNames.add(name.split(@'$').last());
           }
-        } else {
-          fixedMemberNames.add(element.name.slowToString());
         }
+        // Even class names are added due to a delicate problem we have:
+        // if one imports dart:core with a prefix, we cannot tell prefix.name
+        // from dynamic invocation (alas!).  So we'd better err on preserving
+        // those names.
+        fixedMemberNames.add(element.name.slowToString());
       }
     }
     // TODO(antonm): TypeError.srcType and TypeError.dstType are defined in
     // runtime/lib/error.dart. Overall, all DartVM specific libs should be
     // accounted for.
     fixedMemberNames.add('srcType');
     fixedMemberNames.add('dstType');
 
     /**
      * Tells whether we should output given element. Corelib classes like
@@ skipping 205 matching lines @@
 }
 
 compareElements(e0, e1) {
   int result = compareBy((e) => e.getLibrary().uri.toString())(e0, e1);
   if (result != 0) return result;
   return compareBy((e) => e.position().charOffset)(e0, e1);
 }
 
 List<Element> sortElements(Collection<Element> elements) =>
     sorted(elements, compareElements);