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/jdwp/jdwp_handler.cc b/src/jdwp/jdwp_handler.cc
index e8f9e61..355fc5e 100644
--- a/src/jdwp/jdwp_handler.cc
+++ b/src/jdwp/jdwp_handler.cc
@@ -849,7 +849,7 @@
   ObjectId stringObject = ReadObjectId(&buf);
   std::string str(Dbg::StringToUtf8(stringObject));
 
-  VLOG(jdwp) << StringPrintf("  Req for str %#llx --> '%s'", stringObject, PrintableString(str).c_str());
+  VLOG(jdwp) << StringPrintf("  Req for str %#llx --> %s", stringObject, PrintableString(str).c_str());
 
   expandBufAddUtf8String(pReply, str);