Simulates memory stick size to get fixed free space.

Some games may be sensitive to the changes of free space of memory stick, and Android's free space is usually variable.

Core/FileSystems/MetaFileSystem.cpp

@@ -669,3 +669,17 @@ void MetaFileSystem::DoState(PointerWrap &p)
 	}
 }
 
+u64 MetaFileSystem::getDirSize(const std::string &dirPath) {
+	u64 result = 0;
+	auto allFiles = GetDirListing(dirPath);
+	for (auto file : allFiles) {
+		if (file.name == "." || file.name == "..")
+			continue;
+		if (file.type == FILETYPE_DIRECTORY) {
+			result += getDirSize(dirPath + file.name + "/");
+		} else {
+			result += file.size;
+		}
+	}
+	return result;
+}