Fix broken JNI IsAssignableFrom.

The expected argument order was the opposite of what the spec
dictated.

Reported-By: Mikhail Naganov <mnaganov@google.com>
bug: 16531674

Change-Id: I1ebc6d5814ebb4feeb96f3ecdf1a4602da4ba7ce
diff --git a/runtime/jni_internal.cc b/runtime/jni_internal.cc
index d5b90f2..43b9912 100644
--- a/runtime/jni_internal.cc
+++ b/runtime/jni_internal.cc
@@ -677,13 +677,15 @@
     return soa.AddLocalReference<jclass>(c->GetSuperClass());
   }
 
+  // Note: java_class1 should be safely castable to java_class2, and
+  // not the other way around.
   static jboolean IsAssignableFrom(JNIEnv* env, jclass java_class1, jclass java_class2) {
     CHECK_NON_NULL_ARGUMENT_RETURN(java_class1, JNI_FALSE);
     CHECK_NON_NULL_ARGUMENT_RETURN(java_class2, JNI_FALSE);
     ScopedObjectAccess soa(env);
     mirror::Class* c1 = soa.Decode<mirror::Class*>(java_class1);
     mirror::Class* c2 = soa.Decode<mirror::Class*>(java_class2);
-    return c1->IsAssignableFrom(c2) ? JNI_TRUE : JNI_FALSE;
+    return c2->IsAssignableFrom(c1) ? JNI_TRUE : JNI_FALSE;
   }
 
   static jboolean IsInstanceOf(JNIEnv* env, jobject jobj, jclass java_class) {