Fix most warnings and other minor cleanups.

lib/compiler/implementation/operations.dart

Index: lib/compiler/implementation/operations.dart
diff --git a/lib/compiler/implementation/operations.dart b/lib/compiler/implementation/operations.dart
index e445678aa319176291d85c1692f5c8186a78a436..3bd11b8b52bcbd2d19d6b989e7d1d3cc50d5e3c7 100644
--- a/lib/compiler/implementation/operations.dart
+++ b/lib/compiler/implementation/operations.dart
@@ -235,8 +235,7 @@ class AddOperation implements BinaryOperation {
       if (rightDartString.isEmpty()) {
         return left;
       } else if (leftString.value.isEmpty()) {
-        // TODO(floitsch): There is no right.node. Find a node some other way.
-        return new StringConstant(rightDartString, right.node);
+        return new StringConstant(rightDartString, leftString.node);
       } else {
         DartString concatenated =
             new ConsDartString(leftString.value, rightDartString);