AAPT2: Better debugging output

Test: make aapt2_tests
Change-Id: I7778b773201381538dc1f2e376abee4eb33e44c0
diff --git a/tools/aapt2/ConfigDescription.cpp b/tools/aapt2/ConfigDescription.cpp
index 59a6e12..f621660 100644
--- a/tools/aapt2/ConfigDescription.cpp
+++ b/tools/aapt2/ConfigDescription.cpp
@@ -882,6 +882,11 @@
   return std::string(locale);
 }
 
+std::string ConfigDescription::to_string() const {
+  const android::String8 str = toString();
+  return std::string(str.string(), str.size());
+}
+
 bool ConfigDescription::Dominates(const ConfigDescription& o) const {
   if (*this == o) {
     return true;