Add utilities for converting from Host endianity to big endian and little endian formats for the va…

runtime/platform/utils_macos.h

Index: runtime/platform/utils_macos.h
===================================================================
--- runtime/platform/utils_macos.h	(revision 21569)
+++ runtime/platform/utils_macos.h	(working copy)
@@ -5,6 +5,8 @@
 #ifndef PLATFORM_UTILS_MACOS_H_
 #define PLATFORM_UTILS_MACOS_H_
 
+#include <libkern/OSByteOrder.h>  // NOLINT
+
 namespace dart {
 
 inline int Utils::CountTrailingZeros(uword x) {
@@ -17,6 +19,36 @@
 #endif
 };
 
+
+inline uint16_t Utils::HostToBigEndian16(uint16_t value) {
+  return OSSwapHostToBigInt16(value);
+}
+
+
+inline uint32_t Utils::HostToBigEndian32(uint32_t value) {
+  return OSSwapHostToBigInt32(value);
+}
+
+
+inline uint64_t Utils::HostToBigEndian64(uint64_t value) {
+  return OSSwapHostToBigInt64(value);
+}
+
+
+inline uint16_t Utils::HostToLittleEndian16(uint16_t value) {
+  return OSSwapHostToLittleInt16(value);
+}
+
+
+inline uint32_t Utils::HostToLittleEndian32(uint32_t value) {
+  return OSSwapHostToLittleInt32(value);
+}
+
+
+inline uint64_t Utils::HostToLittleEndian64(uint64_t value) {
+  return OSSwapHostToLittleInt64(value);
+}
+
 }  // namespace dart
 
 #endif  // PLATFORM_UTILS_MACOS_H_