message: Use size_t for string size
  This fixes a broken build
diff: @@ -249,14 +249,14 @@ string Uppercase(StringPiece s) {
  }
  string ArgDefCase(StringPiece s) {
  - const int n = s.size();
  + const size_t n = s.size();
  // Compute the size of resulting string.
  // Number of extra underscores we will need to add.
  - int extra_us = 0;
  + size_t extra_us = 0;
  // Number of non-alpha chars in the beginning to skip.
  - int to_skip = 0;
  - for (int i = 0; i < n; ++i) {
  + size_t to_skip = 0;
  + for (size_t i = 0; i < n; ++i) {
  // If we are skipping and current letter is non-alpha, skip it as well
  if (i == to_skip && !isalpha(s[i])) {
  ++to_skip;
  @@ -277,7 +277,7 @@ string ArgDefCase(StringPiece s) {
  string result(n + extra_us - to_skip, '_');
  // i - index into s
  // j - index into result
  - for (int i = to_skip, j = 0; i < n; ++i, ++j) {
  + for (size_t i = to_skip, j = 0; i < n; ++i, ++j) {
  DCHECK_LT(j, result.size());
  char c = s[i];
  // If c is not alphanumeric, we don't need to do anything
  