Add logging to monitor deflation.

Change-Id: I0251ff19e0a3c3b9edc7c7e296f15eb3229f8f7c
diff --git a/runtime/gc/heap.cc b/runtime/gc/heap.cc
index 6c63e5f..296accc 100644
--- a/runtime/gc/heap.cc
+++ b/runtime/gc/heap.cc
@@ -866,7 +866,10 @@
     // about pauses.
     Runtime* runtime = Runtime::Current();
     runtime->GetThreadList()->SuspendAll();
-    runtime->GetMonitorList()->DeflateMonitors();
+    uint64_t start_time = NanoTime();
+    size_t count = runtime->GetMonitorList()->DeflateMonitors();
+    VLOG(heap) << "Deflating " << count << " monitors took "
+        << PrettyDuration(NanoTime() - start_time);
     runtime->GetThreadList()->ResumeAll();
     // Do a heap trim if it is needed.
     Trim();