Android: Show how long ago each savestate was created

Source/Core/Core/State.h

@@ -36,6 +36,9 @@ bool ReadHeader(const std::string& filename, StateHeader& header);
 // which can be presented to the user for identification purposes
 std::string GetInfoStringOfSlot(int slot, bool translate = true);
 
+// Returns when the savestate in the given slot was created, or 0 if the slot is empty.
+u64 GetUnixTimeOfSlot(int slot);
+
 // These don't happen instantly - they get scheduled as events.
 // ...But only if we're not in the main CPU thread.
 //    If we're in the main CPU thread then they run immediately instead