Don't use UTF16 length as length for MUTF8.

Bug 11367555.

Change-Id: Ia0b07072a1a49d435c3b71ed9a668b316b7ff5d8
diff --git a/runtime/debugger.cc b/runtime/debugger.cc
index 57bd57e..4b30a15 100644
--- a/runtime/debugger.cc
+++ b/runtime/debugger.cc
@@ -891,7 +891,7 @@
   }
 
   if (pDescriptor != NULL) {
-    *pDescriptor = ClassHelper(c).GetDescriptorAsStringPiece().as_string();
+    *pDescriptor = ClassHelper(c).GetDescriptor();
   }
   return JDWP::ERR_NONE;
 }
@@ -934,7 +934,7 @@
   if (c == NULL) {
     return status;
   }
-  *signature = ClassHelper(c).GetDescriptorAsStringPiece().as_string();
+  *signature = ClassHelper(c).GetDescriptor();
   return JDWP::ERR_NONE;
 }
 
@@ -2289,7 +2289,7 @@
   int state = JDWP::CS_VERIFIED | JDWP::CS_PREPARED;
   JDWP::JdwpTypeTag tag = c->IsInterface() ? JDWP::TT_INTERFACE : JDWP::TT_CLASS;
   gJdwpState->PostClassPrepare(tag, gRegistry->Add(c),
-                               ClassHelper(c).GetDescriptorAsStringPiece().as_string(), state);
+                               ClassHelper(c).GetDescriptor(), state);
 }
 
 void Dbg::UpdateDebugger(Thread* thread, mirror::Object* this_object,