TimeStats: bound the stats pool size

On any device having TimeStats enabled, the stats pool will be cleared once per
day based on the stats pulling schedule. This change just adds an additional
protect in case the layer count explodes during a tracing period.

Test: TimeStatsTest
Change-Id: I3067239c12645008bceb61a1b7e59d8d6f89076a
diff --git a/services/surfaceflinger/TimeStats/TimeStats.h b/services/surfaceflinger/TimeStats/TimeStats.h
index 2bcb568..eed7111 100644
--- a/services/surfaceflinger/TimeStats/TimeStats.h
+++ b/services/surfaceflinger/TimeStats/TimeStats.h
@@ -161,6 +161,7 @@
     GlobalRecord mGlobalRecord;
 
     static const size_t MAX_NUM_LAYER_RECORDS = 200;
+    static const size_t MAX_NUM_LAYER_STATS = 200;
 };
 
 } // namespace impl