Add locations to diagnostics.

dart/lib/compiler/implementation/operations.dart

Index: dart/lib/compiler/implementation/operations.dart
diff --git a/dart/lib/compiler/implementation/operations.dart b/dart/lib/compiler/implementation/operations.dart
index 3e2d8fb22e45c148b06e1a8e756d0c6b76b6920b..3cc81af5c1520359a16b2f096b0c978366199445 100644
--- a/dart/lib/compiler/implementation/operations.dart
+++ b/dart/lib/compiler/implementation/operations.dart
@@ -235,11 +235,11 @@ class AddOperation implements BinaryOperation {
       if (rightDartString.isEmpty()) {
         return left;
       } else if (leftString.value.isEmpty()) {
-        return new StringConstant(rightDartString);
+        return new StringConstant(rightDartString, right.node);
       } else {
         DartString concatenated =
             new ConsDartString(leftString.value, rightDartString);
-        return new StringConstant(concatenated);
+        return new StringConstant(concatenated, leftString.node);
       }
     } else {
       return null;