Fix compile error on MSAN bot

TBR=reed@google.com

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2142653002

Review-Url: https://codereview.chromium.org/2142653002
diff --git a/tests/RectTest.cpp b/tests/RectTest.cpp
index 719b5b9..6756ee5 100644
--- a/tests/RectTest.cpp
+++ b/tests/RectTest.cpp
@@ -7,6 +7,7 @@
 
 #include "SkBitmap.h"
 #include "SkCanvas.h"
+#include "SkRandom.h"
 #include "SkRect.h"
 #include "Test.h"