Fix minified signature generation.

sdk/lib/_internal/compiler/implementation/js_backend/emitter.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.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 1349 matching lines @@
     void generateFunctionTypeSignature(Element method, FunctionType type) {
       assert(method.isImplementation);
       String thisAccess = 'this';
       Node node = method.parseNode(compiler);
       ClosureClassMap closureData =
           compiler.closureToClassMapper.closureMappingCache[node];
       if (closureData != null) {
         Element thisElement =
             closureData.freeVariableMapping[closureData.thisElement];
         if (thisElement != null) {
-          String thisName = backend.namer.getName(thisElement);
+          assert(thisElement.hasFixedBackendName());
+          String thisName = thisElement.fixedBackendName();
           thisAccess = 'this.$thisName';
         }
       }
       RuntimeTypes rti = backend.rti;
       String encoding = rti.getSignatureEncoding(type, () => '$thisAccess');
       String operatorSignature = namer.operatorSignature();
       builder.addProperty(operatorSignature,
           new jsAst.LiteralExpression(encoding));
     }
 
@@ skipping 2319 matching lines @@
 
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;