Always enable checkjni in debug builds.

Would have help show the issue for b/218518604

Test: m
Change-Id: If56d47dc58abd9916a81254883e956e23cb5b095
diff --git a/runtime/jni/java_vm_ext.cc b/runtime/jni/java_vm_ext.cc
index 94108c6..df7375b 100644
--- a/runtime/jni/java_vm_ext.cc
+++ b/runtime/jni/java_vm_ext.cc
@@ -516,7 +516,7 @@
       allocation_tracking_enabled_(false),
       old_allocation_tracking_state_(false) {
   functions = unchecked_functions_;
-  SetCheckJniEnabled(runtime_options.Exists(RuntimeArgumentMap::CheckJni));
+  SetCheckJniEnabled(runtime_options.Exists(RuntimeArgumentMap::CheckJni) || kIsDebugBuild);
 }
 
 JavaVMExt::~JavaVMExt() {