libutils: disable implicit ref base construction

Ignore-AOSP-First: b/184196278

Bug: 184190315
Test: libutils_test
Change-Id: If47f79a8b96ee75706817081950f9ca5c0d12731
diff --git a/libutils/Threads.cpp b/libutils/Threads.cpp
index 540dcf4..1c8f810 100644
--- a/libutils/Threads.cpp
+++ b/libutils/Threads.cpp
@@ -693,7 +693,7 @@
     mThread = thread_id_t(-1);
 
     // hold a strong reference on ourself
-    mHoldSelf = this;
+    mHoldSelf = sp<Thread>::fromExisting(this);
 
     mRunning = true;