[heap] Fix ObjectStats compile on Android/GN

NOTRY=true
TBR=ulan@chromium.org

Review-Url: https://codereview.chromium.org/2150563002
Cr-Commit-Position: refs/heads/master@{#37720}

src/heap/object-stats.h

@@ -5,6 +5,8 @@
 #ifndef V8_HEAP_OBJECT_STATS_H_
 #define V8_HEAP_OBJECT_STATS_H_
 
+#include <math.h>
+
 #include "src/heap/heap.h"
 #include "src/heap/objects-visiting.h"
 #include "src/objects.h"