Many type fixes.

lib/compiler/implementation/compile_time_constants.dart

Index: lib/compiler/implementation/compile_time_constants.dart
diff --git a/lib/compiler/implementation/compile_time_constants.dart b/lib/compiler/implementation/compile_time_constants.dart
index d660d9e1694c2c339138bdead8ae01a1561743a9..1f4b57fb4b4712149c90d05a3d7a8f9c74c7f7e2 100644
--- a/lib/compiler/implementation/compile_time_constants.dart
+++ b/lib/compiler/implementation/compile_time_constants.dart
@@ -795,10 +795,11 @@ class CompileTimeConstantEvaluator extends AbstractVisitor {
       Constant expression = evaluate(part.expression);
       DartString expressionString;
       if (expression.isNum() || expression.isBool()) {
-        Object value = expression.value;
-        expressionString = new DartString.literal(value.toString());
+        PrimitiveConstant primitive = expression;
+        expressionString = new DartString.literal(primitive.value.toString());
       } else if (expression.isString()) {
-        expressionString = expression.value;
+        PrimitiveConstant primitive = expression;
+        expressionString = primitive.value;
       } else {
         error(part.expression);
       }