Use PrintableString in oatdump.

And enhance PrintableString to assume modified UTF-8, which is all we ever give
it. \u0000 is more readable than \xc0\x80 to most people.

Change-Id: I45bd8d65694eda0ef4ef03abc40f41a76f07a671
diff --git a/src/class_linker.cc b/src/class_linker.cc
index ae13908..4a38493 100644
--- a/src/class_linker.cc
+++ b/src/class_linker.cc
@@ -1216,7 +1216,7 @@
     }
   }
 
-  ThrowNoClassDefFoundError("Class %s not found", PrintableString(StringPiece(descriptor)).c_str());
+  ThrowNoClassDefFoundError("Class %s not found", PrintableString(descriptor).c_str());
   return NULL;
 }