A local may be an unnamed closure. Make sure we emit a name for them.

frog/leg/ssa/codegen.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.
 
 class SsaCodeGeneratorTask extends CompilerTask {
   SsaCodeGeneratorTask(Compiler compiler) : super(compiler);
   String get name() => 'SSA code generator';
 
   String generate(WorkItem work, HGraph graph) {
     return measure(() {
@@ skipping 168 matching lines @@
   String local(HLocal local) {
     Element element = local.element;
     if (element != null && element.kind == ElementKind.PARAMETER) {
       return parameterNames[element];
     }
     int id = local.id;
     String name = names[id];
     if (name !== null) return name;
 
     String prefix;
-    if (element !== null) {
+    if (element !== null && !element.name.isEmpty()) {
       prefix = element.name.slowToString();
     } else {
       prefix = 'v';
     }
     if (!prefixes.containsKey(prefix)) {
       prefixes[prefix] = 0;
       return newName(id, prefix);
     } else {
       return newName(id, '${prefix}_${prefixes[prefix]++}');
     }
@@ skipping 464 matching lines @@
     // need to work together to avoid the parenthesis. See r4928 for an
     // implementation that still dealt with precedence.
     ConstantHandler handler = compiler.constantHandler;
     String name = handler.getNameForConstant(node.constant);
     if (name === null) {
       assert(!node.constant.isObject());
       node.constant.writeJsCode(buffer, handler);
     } else {
       buffer.add(compiler.namer.CURRENT_ISOLATE);
       buffer.add(".");
-      buffer.add(name);      
+      buffer.add(name);
     }
   }
 
   visitLoopBranch(HLoopBranch node) {
     HBasicBlock branchBlock = currentBlock;
     handleLoopCondition(node);
     List<HBasicBlock> dominated = currentBlock.dominatedBlocks;
     // For a do while loop, the body has already been visited.
     if (!node.isDoWhile()) {
       visitBasicBlock(dominated[0]);
@@ skipping 707 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endElse(HIf node) {
     if (node.elseBlock.hasBailouts()) {
       endBailoutSwitch();
     }
   }
 }