Fast JNI support.

Use a modifier to signal a native method is a fast JNI method. If the
modifier is set then don't perform runnable transitions.

Change-Id: I7835b4d837bfdd1cb8e2d54b919c0d5e6cf90499
diff --git a/runtime/jni_internal.h b/runtime/jni_internal.h
index c73ed48..888d5e5 100644
--- a/runtime/jni_internal.h
+++ b/runtime/jni_internal.h
@@ -73,7 +73,7 @@
    * human-readable description of the error.
    */
   bool LoadNativeLibrary(const std::string& path, mirror::ClassLoader* class_loader,
-                         std::string& detail)
+                         std::string* detail)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   /**