Landing patch set 7 from https://codereview.chromium.org/1450113003/

runtime/platform/utils_macos.h

Index: runtime/platform/utils_macos.h
diff --git a/runtime/platform/utils_macos.h b/runtime/platform/utils_macos.h
index 3fa2984991dbbaa79f25bf36714dd43e60f9cc22..7c2a966db9d99f7ca3587224946e9ee0023c907e 100644
--- a/runtime/platform/utils_macos.h
+++ b/runtime/platform/utils_macos.h
@@ -60,6 +60,13 @@ inline uint64_t Utils::HostToLittleEndian64(uint64_t value) {
   return OSSwapHostToLittleInt64(value);
 }
 
+inline char* Utils::StrError(int err, char* buffer, size_t bufsize) {
+  if (strerror_r(err, buffer, bufsize) != 0) {
+    snprintf(buffer, bufsize, "%s", "strerror_r failed");
+  }
+  return buffer;
+}
+
 }  // namespace dart
 
 #endif  // PLATFORM_UTILS_MACOS_H_