dart2js: Support new const operations on strings.

sdk/lib/_internal/compiler/implementation/compile_time_constants.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 dart2js;
 
 /// A [ConstantEnvironment] provides access for constants compiled for variable
 /// initializers.
 abstract class ConstantEnvironment {
   /// Returns the constant for the initializer of [element].
@@ skipping 391 matching lines @@
         if (element.isConst) {
           result = handler.compileConstant(element);
         } else if (element.isFinal && !isEvaluatingConstant) {
           result = handler.compileVariable(element);
         }
         if (result != null) return result;
       } else if (Elements.isClass(element) || Elements.isTypedef(element)) {
         assert(elements.isTypeLiteral(send));
         return makeTypeConstant(elements.getTypeLiteralType(send));
       } else if (send.receiver != null) {
+        if (send.selector.asIdentifier().source == "length") {
+          Constant left = evaluate(send.receiver);
+          if (left != null && left.isString) {
+            StringConstant string = left;
+            return constantSystem.createInt(string.value.length);
+          }
+        }
         // Fall through to error handling.
       } else if (!Elements.isUnresolved(element)
                  && element.isVariable
                  && element.isConst) {
         Constant result = handler.compileConstant(element);
         if (result != null) return result;
       }
       return signalNotCompileTimeConstant(send);
     } else if (send.isCall) {
-      if (identical(element, compiler.identicalFunction)
+      if (element == compiler.identicalFunction
           && send.argumentCount() == 2) {
         Constant left = evaluate(send.argumentsNode.nodes.head);
         Constant right = evaluate(send.argumentsNode.nodes.tail.head);
         Constant result = constantSystem.identity.fold(left, right);
         if (result != null) return result;
       }
       return signalNotCompileTimeConstant(send);
     } else if (send.isPrefix) {
       assert(send.isOperator);
       Constant receiverConstant = evaluate(send.receiver);
@@ skipping 436 matching lines @@
           if (fieldValue == null) {
             // Use the default value.
             fieldValue = handler.compileConstant(field);
           }
           jsNewArguments.add(fieldValue);
         },
         includeSuperAndInjectedMembers: true);
     return jsNewArguments;
   }
 }