Avoid copying and strlen(3) in the FindClass path.

Change-Id: I789f3c883596d1852a2c1954ce7a207e6f937117
diff --git a/src/debugger.cc b/src/debugger.cc
index 4cfc34e..7561560 100644
--- a/src/debugger.cc
+++ b/src/debugger.cc
@@ -550,7 +550,7 @@
   return true;
 }
 
-void Dbg::FindLoadedClassBySignature(const std::string& descriptor, std::vector<JDWP::RefTypeId>& ids) {
+void Dbg::FindLoadedClassBySignature(const char* descriptor, std::vector<JDWP::RefTypeId>& ids) {
   std::vector<Class*> classes;
   Runtime::Current()->GetClassLinker()->LookupClasses(descriptor, classes);
   ids.clear();