Adding method to create process using LowBox token in sandbox code.

sandbox/win/src/sandbox_policy_base.h

Index: sandbox/win/src/sandbox_policy_base.h
diff --git a/sandbox/win/src/sandbox_policy_base.h b/sandbox/win/src/sandbox_policy_base.h
index 54b0b0bc0d864d695cff401d5f66bdf9743c582d..ea0f3e6d5e1a22cf6c4f6b00f952471b142bcde0 100644
--- a/sandbox/win/src/sandbox_policy_base.h
+++ b/sandbox/win/src/sandbox_policy_base.h
@@ -56,6 +56,7 @@ class PolicyBase : public Dispatcher, public TargetPolicy {
       IntegrityLevel integrity_level) override;
   virtual ResultCode SetAppContainer(const wchar_t* sid) override;
   virtual ResultCode SetCapability(const wchar_t* sid) override;
+  virtual ResultCode SetLowBox(const wchar_t* sid) override;
   virtual ResultCode SetProcessMitigations(MitigationFlags flags) override;
   virtual MitigationFlags GetProcessMitigations() override;
   virtual ResultCode SetDelayedProcessMitigations(
@@ -86,6 +87,8 @@ class PolicyBase : public Dispatcher, public TargetPolicy {
 
   const AppContainerAttributes* GetAppContainer() const;
 
+  const PSID GetLowBoxSid() const;
+
   // Adds a target process to the internal list of targets. Internally a
   // call to TargetProcess::Init() is issued.
   bool AddTarget(TargetProcess* target);
@@ -158,6 +161,7 @@ class PolicyBase : public Dispatcher, public TargetPolicy {
   HandleCloser handle_closer_;
   std::vector<base::string16> capabilities_;
   scoped_ptr<AppContainerAttributes> appcontainer_list_;
+  PSID lowbox_sid_;
 
   static HDESK alternate_desktop_handle_;
   static HWINSTA alternate_winstation_handle_;