[dart:io] Adds Platform.operatingSystemVersion

runtime/bin/platform.h

Index: runtime/bin/platform.h
diff --git a/runtime/bin/platform.h b/runtime/bin/platform.h
index dfe9cde9a06699623da499c9c776cddb21563a3e..d174902ad4ff82f628ddcea356060a6710a359fb 100644
--- a/runtime/bin/platform.h
+++ b/runtime/bin/platform.h
@@ -24,6 +24,11 @@ class Platform {
   // deallocated by the caller.
   static const char* OperatingSystem();
 
+  // Returns a string representing the version of the operating system. The
+  // format of the string is determined by the platform. The returned string
+  // should not be deallocated by the caller.
+  static const char* OperatingSystemVersion();
+
   // Returns the architecture name of the processor the VM is running on
   // (ia32, x64, arm, or arm64).
   static const char* HostArchitecture() {