Don't default-construct std::strings and then assign them.

Change-Id: I8c994d1e6a8d2ebe52eaa4f0132e0deb2ecfa5f3
diff --git a/src/object.cc b/src/object.cc
index 9e84327..1ef7201 100644
--- a/src/object.cc
+++ b/src/object.cc
@@ -800,9 +800,9 @@
   }
   // Compare the package part of the descriptor string.
   ClassHelper kh(klass1);
-  std::string descriptor1 = kh.GetDescriptor();
+  std::string descriptor1(kh.GetDescriptor());
   kh.ChangeClass(klass2);
-  std::string descriptor2 = kh.GetDescriptor();
+  std::string descriptor2(kh.GetDescriptor());
   return IsInSamePackage(descriptor1, descriptor2);
 }