dart2js: Support new const operations on strings.

pkg/compiler/lib/src/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 491 matching lines @@
         }
         if (result != null) {
           return new AstConstant(
               context, send,
               new VariableConstantExpression(result.value, element));
         }
       } else if (Elements.isClass(element) || Elements.isTypedef(element)) {
         assert(elements.isTypeLiteral(send));
         return makeTypeConstant(send, elements.getTypeLiteralType(send));
       } else if (send.receiver != null) {
+        if (send.selector.asIdentifier().source == "length") {
+          AstConstant left = evaluate(send.receiver);
+          if (left != null && left.value.isString) {
+            StringConstantValue stringConstantValue = left.value;
+            DartString string = stringConstantValue.primitiveValue;
+            IntConstantValue length = constantSystem.createInt(string.length);
+            return new AstConstant(
+                context, send, new VariableConstantExpression(length, element));
+          }
+        }
         // Fall through to error handling.
       } else if (!Elements.isUnresolved(element)
                  && element.isVariable
                  && element.isConst) {
         ConstantExpression result = handler.compileConstant(element);
         if (result != null) {
           return new AstConstant(
               context, send,
               new VariableConstantExpression(result.value, element));
         }
       }
       return signalNotCompileTimeConstant(send);
     } else if (send.isCall) {
-      if (identical(element, compiler.identicalFunction)
+      if (element == compiler.identicalFunction
           && send.argumentCount() == 2) {
         AstConstant left = evaluate(send.argumentsNode.nodes.head);
         AstConstant right = evaluate(send.argumentsNode.nodes.tail.head);
         if (left == null || right == null) {
           return null;
         }
         ConstantValue result =
             constantSystem.identity.fold(left.value, right.value);
         if (result != null) {
           return new AstConstant(
@@ skipping 565 matching lines @@
     return new AstConstant(
         element,
         element.initializer != null ? element.initializer : element.node,
         constant);
   }
 
   ConstantValue get value => expression.value;
 
   String toString() => expression.toString();
 }