Add signal handler for low disk notification

chromeos/dbus/cryptohome_client.h

Index: chromeos/dbus/cryptohome_client.h
diff --git a/chromeos/dbus/cryptohome_client.h b/chromeos/dbus/cryptohome_client.h
index 15ce84f5e9fb43c6584304f32d4f19b5e48a8604..cc0fd7025da37aa4e2bafa1f74580a201d27f9be 100644
--- a/chromeos/dbus/cryptohome_client.h
+++ b/chromeos/dbus/cryptohome_client.h
@@ -62,6 +62,8 @@ class CHROMEOS_EXPORT CryptohomeClient : public DBusClient {
   typedef base::Callback<void(DBusMethodCallStatus call_status,
                               const std::vector<uint8_t>& system_salt)>
       GetSystemSaltCallback;
+  // A callback to handle LowDiskSpace signals.
+  typedef base::Callback<void(uint64_t disk_free_bytes)> LowDiskSpaceHandler;
   // A callback for WaitForServiceToBeAvailable().
   typedef base::Callback<void(bool service_is_ready)>
       WaitForServiceToBeAvailableCallback;
@@ -110,6 +112,10 @@ class CHROMEOS_EXPORT CryptohomeClient : public DBusClient {
   // Resets AsyncCallStatus signal handlers.
   virtual void ResetAsyncCallStatusHandlers() = 0;
 
+  // Sets LowDiskSpace signal handler.  |handler| is called when the cryptohome
+  // partition is running out of disk space.
+  virtual void SetLowDiskSpaceHandler(const LowDiskSpaceHandler& handler) = 0;
+
   // Runs the callback as soon as the service becomes available.
   virtual void WaitForServiceToBeAvailable(
       const WaitForServiceToBeAvailableCallback& callback) = 0;