Clean up Handle usage.

Prefer using ConstHandle instead of Handle as function arguments
since you can't assign new references to ConstHandle which helps
prevent bugs.

Changed NullHandle to be a ConstHandle so that you can never modify
it to be a non null reference.

Change-Id: I81cb979f6f8d5b49e5614966a2caf28c3701dd4f
diff --git a/runtime/interpreter/interpreter_common.cc b/runtime/interpreter/interpreter_common.cc
index 6705695..74fa981 100644
--- a/runtime/interpreter/interpreter_common.cc
+++ b/runtime/interpreter/interpreter_common.cc
@@ -764,8 +764,8 @@
 }
 
 // Helper function to deal with class loading in an unstarted runtime.
-static void UnstartedRuntimeFindClass(Thread* self, Handle<mirror::String> className,
-                                      Handle<mirror::ClassLoader> class_loader, JValue* result,
+static void UnstartedRuntimeFindClass(Thread* self, ConstHandle<mirror::String> className,
+                                      ConstHandle<mirror::ClassLoader> class_loader, JValue* result,
                                       const std::string& method_name, bool initialize_class,
                                       bool abort_if_not_found)
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {