Stop treating final as const in dart2js.

lib/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.
 
 /**
  * The [ConstantHandler] keeps track of compile-time constants,
  * initializations of global and static fields, and default values of
  * optional parameters.
  */
 class ConstantHandler extends CompilerTask {
@@ skipping 349 matching lines @@
         new DartString.concat(left.value, right.value), node);
   }
 
   Constant visitStringInterpolation(StringInterpolation node) {
     StringConstant initialString = evaluate(node.string);
     if (initialString == null) return null;
     DartString accumulator = initialString.value;
     for (StringInterpolationPart part in node.parts) {
       Constant expression = evaluate(part.expression);
       DartString expressionString;
-      if (expression.isNum() || expression.isBool()) {
+      if (expression === null) {
+        return signalNotCompileTimeConstant(part.expression);
+      } else if (expression.isNum() || expression.isBool()) {
         PrimitiveConstant primitive = expression;
         expressionString = new DartString.literal(primitive.value.toString());
       } else if (expression.isString()) {
         PrimitiveConstant primitive = expression;
         expressionString = primitive.value;
       } else {
         return signalNotCompileTimeConstant(part.expression);
       }
       accumulator = new DartString.concat(accumulator, expressionString);
       StringConstant partString = evaluate(part.string);
       if (partString == null) return null;
       accumulator = new DartString.concat(accumulator, partString.value);
     };
     return constantSystem.createString(accumulator, node);
   }
 
   // TODO(floitsch): provide better error-messages.
   Constant visitSend(Send send) {
     Element element = elements[send];
     if (Elements.isStaticOrTopLevelField(element)) {
       Constant result;
       if (element.modifiers !== null) {
         if (element.modifiers.isConst()) {
           result = compiler.compileConstant(element);
-        } else if (element.modifiers.isFinal()) {
-          // TODO(4516): remove support for final compile-time constants: if
-          // isCompilingConstant is true don't compile the variable.
+        } else if (element.modifiers.isFinal() && !isEvaluatingConstant) {
           result = compiler.compileVariable(element);
         }
       }
       if (result == null) return signalNotCompileTimeConstant(send);
       return result;
     } else if (Elements.isStaticOrTopLevelFunction(element)
                && send.isPropertyAccess) {
       compiler.codegenWorld.staticFunctionsNeedingGetter.add(element);
       Constant constant = new FunctionConstant(element);
       compiler.constantHandler.registerCompileTimeConstant(constant);
@@ skipping 346 matching lines @@
       Constant fieldValue = fieldValues[field];
       if (fieldValue === null) {
         // Use the default value.
         fieldValue = compiler.compileConstant(field);
       }
       jsNewArguments.add(fieldValue);
     });
     return jsNewArguments;
   }
 }