Reapply directory error handling change.

runtime/bin/platform.h

Index: runtime/bin/platform.h
diff --git a/runtime/bin/platform.h b/runtime/bin/platform.h
index e4e30aa4100a62f009a2f8e12a759cadebfacb83..b6aa090b5b88d13935a6ec7f511137ef817c950e 100644
--- a/runtime/bin/platform.h
+++ b/runtime/bin/platform.h
@@ -9,9 +9,18 @@
 
 class Platform {
  public:
+  // Returns the number of processors on the machine.
   static int NumberOfProcessors();
+
+  // Returns a string representing the operating system ("linux",
+  // "macos" or "windows"). The returned string should not be
+  // deallocated by the caller.
   static const char* OperatingSystem();
 
+  // Returns a string representation of an error code. The returned
+  // string must be deallocated by the caller.
+  static char* StrError(int error_code);
+
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Platform);