ART: Fix inefficent find/rfind

Use character instead of string versions where possible.

Bug: 32619234
Test: m test-art-host
Change-Id: Ifa0a68f17cf9fac5a8c15a6a1f1d085f0c8dcdd7
diff --git a/test/ti-stress/stress.cc b/test/ti-stress/stress.cc
index 06d5af0..5d7c2f3 100644
--- a/test/ti-stress/stress.cc
+++ b/test/ti-stress/stress.cc
@@ -533,7 +533,7 @@
     return;
   }
   std::string type(method_info.GetSignature());
-  type = type.substr(type.find(")") + 1);
+  type = type.substr(type.find(')') + 1);
   std::string out_val(was_popped_by_exception ? "" : GetValOf(jvmtienv, env, type, val));
   LOG(INFO) << "Leaving method \"" << method_info << "\". Thread is \"" << info.GetName() << "\"."
             << std::endl