ART: Add OnLoad system classloader search support

Add support for extension of the system classloader search path
during the OnLoad phase. Add test.

Bug: 34359699
Test: m test-art-host-run-test-936-search-onload
Change-Id: Ie0a5b4bb77999dfae87f955dde40b73ffe053b8e
diff --git a/runtime/openjdkjvmti/ti_phase.cc b/runtime/openjdkjvmti/ti_phase.cc
index 4970288..60371cf 100644
--- a/runtime/openjdkjvmti/ti_phase.cc
+++ b/runtime/openjdkjvmti/ti_phase.cc
@@ -136,4 +136,8 @@
   art::Runtime::Current()->GetRuntimeCallbacks()->RemoveRuntimePhaseCallback(&gPhaseCallback);
 }
 
+jvmtiPhase PhaseUtil::GetPhaseUnchecked() {
+  return PhaseUtil::current_phase_;
+}
+
 }  // namespace openjdkjvmti