add missing include

CQ_INCLUDE_TRYBOTS=master.client.skia:Perf-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-MSAN-Trybot

Review-Url: https://codereview.chromium.org/2226783002
diff --git a/tests/ChecksumTest.cpp b/tests/ChecksumTest.cpp
index 2aaf268..1882235 100644
--- a/tests/ChecksumTest.cpp
+++ b/tests/ChecksumTest.cpp
@@ -5,6 +5,7 @@
  * found in the LICENSE file.
  */
 
+#include "SkChecksum.h"
 #include "SkOpts.h"
 #include "SkRandom.h"
 #include "Test.h"