Fix a couple of warnings from MSVC.

Change-Id: I7b67d47eb5028491279f543670262bf6d13693a9
Reviewed-on: https://code-review.googlesource.com/4237
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/re2/testing/re2_test.cc b/re2/testing/re2_test.cc
index 0391e0a..5a32d92 100644
--- a/re2/testing/re2_test.cc
+++ b/re2/testing/re2_test.cc
@@ -1583,10 +1583,10 @@
   string s = "abc";
   StringPiece m;
 
-  CHECK(re.Match(s, 0, s.size(), RE2::UNANCHORED, &m, 1));
+  CHECK(re.Match(s, 0, static_cast<int>(s.size()), RE2::UNANCHORED, &m, 1));
   CHECK_EQ(m, s) << " (UNANCHORED) got m='" << m << "', want '" << s << "'";
 
-  CHECK(re.Match(s, 0, s.size(), RE2::ANCHOR_BOTH, &m, 1));
+  CHECK(re.Match(s, 0, static_cast<int>(s.size()), RE2::ANCHOR_BOTH, &m, 1));
   CHECK_EQ(m, s) << " (ANCHOR_BOTH) got m='" << m << "', want '" << s << "'";
 }