Add helpers library to dart2js.

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;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 1816 matching lines @@
     bool hasNoThrows = false;
     bool hasNoSideEffects = false;
     for (MetadataAnnotation metadata in element.metadata) {
       metadata.ensureResolved(compiler);
       if (!metadata.value.isConstructedObject) continue;
       ObjectConstant value = metadata.value;
       ClassElement cls = value.type.element;
       if (cls == noInlineClass) {
         hasNoInline = true;
         if (VERBOSE_OPTIMIZER_HINTS) {
-          compiler.reportHere(element, "Cannot inline");
+          compiler.reportHint(element,
+              MessageKind.GENERIC,
+              {'text': "Cannot inline"});
         }
         inlineCache.markAsNonInlinable(element);
       } else if (cls == noThrowsClass) {
         hasNoThrows = true;
         if (!Elements.isStaticOrTopLevelFunction(element)) {
           compiler.internalError(element,
               "@NoThrows() is currently limited to top-level"
               " or static functions");
         }
         if (VERBOSE_OPTIMIZER_HINTS) {
-          compiler.reportHere(element, "Cannot throw");
+          compiler.reportHint(element,
+              MessageKind.GENERIC,
+              {'text': "Cannot throw"});
         }
         compiler.world.registerCannotThrow(element);
       } else if (cls == noSideEffectsClass) {
         hasNoSideEffects = true;
         if (VERBOSE_OPTIMIZER_HINTS) {
-          compiler.reportHere(element, "Has no side effects");
+          compiler.reportHint(element,
+              MessageKind.GENERIC,
+              {'text': "Has no side effects"});
         }
         compiler.world.registerSideEffectsFree(element);
       }
     }
     if (hasNoThrows && !hasNoInline) {
       compiler.internalError(element,
           "@NoThrows() should always be combined with @NoInline.");
     }
     if (hasNoSideEffects && !hasNoInline) {
       compiler.internalError(element,
           "@NoSideEffects() should always be combined with @NoInline.");
     }
   }
 
   CodeBuffer codeOf(Element element) {
     return generatedCode.containsKey(element)
         ? jsAst.prettyPrint(generatedCode[element], compiler)
         : null;
   }
 }
 
 /// Records that [constant] is used by [user.element].
 class Dependency {
   final Constant constant;
   final TreeElements user;
 
   const Dependency(this.constant, this.user);
 }
 
-/// Used to copy metadata to the the actual constant handler.
-class ConstantCopier implements ConstantVisitor {
-  final ConstantHandler target;
-
-  ConstantCopier(this.target);
-
-  void copy(/* Constant or List<Constant> */ value) {
-    if (value is Constant) {
-      target.compiledConstants.add(value);
-    } else {
-      target.compiledConstants.addAll(value);
-    }
-  }
-
-  void visitFunction(FunctionConstant constant) => copy(constant);
-
-  void visitNull(NullConstant constant) => copy(constant);
-
-  void visitInt(IntConstant constant) => copy(constant);
-
-  void visitDouble(DoubleConstant constant) => copy(constant);
-
-  void visitTrue(TrueConstant constant) => copy(constant);
-
-  void visitFalse(FalseConstant constant) => copy(constant);
-
-  void visitString(StringConstant constant) => copy(constant);
-
-  void visitType(TypeConstant constant) => copy(constant);
-
-  void visitInterceptor(InterceptorConstant constant) => copy(constant);
-
-  void visitDummy(DummyConstant constant) => copy(constant);
-
-  void visitList(ListConstant constant) {
-    copy(constant.entries);
-    copy(constant);
-  }
-  void visitMap(MapConstant constant) {
-    copy(constant.keys);
-    copy(constant.values);
-    copy(constant.protoValue);
-    copy(constant);
-  }
-
-  void visitConstructed(ConstructedConstant constant) {
-    copy(constant.fields);
-    copy(constant);
-  }
-}