ART: Fix systrace monitor logging

Thinlock unlocking was incorrectly unconditionally ending a block.

Bug: 28423466

(cherry picked from commit 825ab1c3f44fd84e5967f023c2dd8d36c6906f08)

Change-Id: Ifaebd9e959041e157e292d4cba05675a37e9c700
diff --git a/runtime/monitor.cc b/runtime/monitor.cc
index f4bc222..71c866f 100644
--- a/runtime/monitor.cc
+++ b/runtime/monitor.cc
@@ -964,17 +964,13 @@
           if (!kUseReadBarrier) {
             DCHECK_EQ(new_lw.ReadBarrierState(), 0U);
             h_obj->SetLockWord(new_lw, true);
-            if (ATRACE_ENABLED()) {
-              ATRACE_END();
-            }
+            AtraceMonitorUnlock();
             // Success!
             return true;
           } else {
             // Use CAS to preserve the read barrier state.
             if (h_obj->CasLockWordWeakSequentiallyConsistent(lock_word, new_lw)) {
-              if (ATRACE_ENABLED()) {
-                ATRACE_END();
-              }
+              AtraceMonitorUnlock();
               // Success!
               return true;
             }