Support general expressions as keys in literal maps.

sdk/lib/_internal/compiler/implementation/js_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.
 
 part of js_backend;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked;
 
   JavaScriptItemCompilationContext()
@@ skipping 1123 matching lines @@
     helpersUsed.add(cls.declaration);
     // Both declaration and implementation may declare fields, so we
     // add both to the list of helpers.
     if (cls.declaration != cls.implementation) {
       helpersUsed.add(cls.implementation);
     }
     enqueuer.registerInstantiatedClass(cls, elements);
   }
 
   void registerConstantMap(TreeElements elements) {
-    Element e = compiler.findHelper(const SourceString('ConstantMap'));
-    if (e != null) {
-      enqueueClass(compiler.enqueuer.resolution, e, elements);
+    void enqueue(SourceString name) {
+      Element e = compiler.findHelper(name);
+      if (e != null) {
+        enqueueClass(compiler.enqueuer.resolution, e, elements);
+      }
     }
-    e = compiler.findHelper(const SourceString('ConstantProtoMap'));
-    if (e != null) {
-      enqueueClass(compiler.enqueuer.resolution, e, elements);
-    }
+
+    enqueue(MapConstant.DART_CLASS);
+    enqueue(MapConstant.DART_PROTO_CLASS);
+    enqueue(MapConstant.DART_STRING_CLASS);
+    enqueue(MapConstant.DART_GENERAL_CLASS);
   }
 
   void codegen(CodegenWorkItem work) {
     Element element = work.element;
     var kind = element.kind;
     if (kind == ElementKind.TYPEDEF) return;
     if (element.isConstructor() && element.getEnclosingClass() == jsNullClass) {
       // Work around a problem compiling JSNull's constructor.
       return;
     }
@@ skipping 617 matching lines @@
     copy(constant.values);
     copy(constant.protoValue);
     copy(constant);
   }
 
   void visitConstructed(ConstructedConstant constant) {
     copy(constant.fields);
     copy(constant);
   }
 }