Avoid 64 bit truncation errors from the compiler for hash

While not possible the compiler still generates errors without
casts.

BUG=879657

Change-Id: I1975197135c8ab2bd0723360180d851b8be17e93
Reviewed-on: https://chromium-review.googlesource.com/c/1348954Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610615}

base/hash.h

@@ -47,7 +47,8 @@ inline size_t HashInts(T1 value1, T2 value2) {
   if (sizeof(T1) > sizeof(uint32_t) || (sizeof(T2) > sizeof(uint32_t)))
     return HashInts64(value1, value2);
 
-  return HashInts32(value1, value2);
+  return HashInts32(static_cast<uint32_t>(value1),
+                    static_cast<uint32_t>(value2));
 }
 
 // A templated hasher for pairs of integer types. Example: