Namespace sandbox: add important security checks

sandbox/linux/services/credentials.h

Index: sandbox/linux/services/credentials.h
diff --git a/sandbox/linux/services/credentials.h b/sandbox/linux/services/credentials.h
index a52617690bd0d877299a745f4bfc15195f9ca3f7..5121602a9f46534262c0fa6415bdbe8f68e885b5 100644
--- a/sandbox/linux/services/credentials.h
+++ b/sandbox/linux/services/credentials.h
@@ -26,7 +26,8 @@ namespace sandbox {
 class SANDBOX_EXPORT Credentials {
  public:
   // Drop all capabilities in the effective, inheritable and permitted sets for
-  // the current process.
+  // the current process. For security reasons, the caller is responsible
+  // for ensuring it is single threaded when calling this API.

[rickyz (no longer on Chrome), 2015/02/11 22:59:56]

It might be good to explicitly mention the reason - that capabilities are
per-thread

[jln (very slow on Chromium), 2015/02/11 23:13:07]

Done.

   static bool DropAllCapabilities() WARN_UNUSED_RESULT;
   // Return true iff there is any capability in any of the capabilities sets
   // of the current process.