Fix ASAN warning.

BUG=
TBR=ishell@chromium.org

Review URL: https://codereview.chromium.org/683033002

Cr-Commit-Position: refs/heads/master@{#24920}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24920 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/cctest/test-utils.cc

@@ -113,6 +113,7 @@ TEST(BitSetComputer) {
     unsigned char data = buffer[index];
     CHECK_EQ(i % 4, TwoBits::decode(data, i));
   }
+  buffer.Dispose();
 }