AAPT2: Fix overlay support

Supports the <add-resource> tag and mimics old AAPT behavior of
not allowing new resources defined unless <add-resource> was used
or --auto-add-overlay was specified.

Change-Id: I9b461137357617ade37fd7045b418b8e6450b9c4
diff --git a/tools/aapt2/NameMangler.h b/tools/aapt2/NameMangler.h
index 6d752bb..054b9ee 100644
--- a/tools/aapt2/NameMangler.h
+++ b/tools/aapt2/NameMangler.h
@@ -60,7 +60,7 @@
         };
     }
 
-    bool shouldMangle(const std::u16string& package) {
+    bool shouldMangle(const std::u16string& package) const {
         if (package.empty() || mPolicy.targetPackageName == package) {
             return false;
         }