libprocessgroup: Use pid_t consistently for TIDs

Test: m
Change-Id: I6e95870e6c5855bfe03be3be8f7a8884147bc15d
diff --git a/libprocessgroup/cgroup_map.h b/libprocessgroup/cgroup_map.h
index 5cdf8b2..5c6d3e2 100644
--- a/libprocessgroup/cgroup_map.h
+++ b/libprocessgroup/cgroup_map.h
@@ -43,7 +43,8 @@
 
     std::string GetTasksFilePath(const std::string& path) const;
     std::string GetProcsFilePath(const std::string& path, uid_t uid, pid_t pid) const;
-    bool GetTaskGroup(int tid, std::string* group) const;
+    bool GetTaskGroup(pid_t tid, std::string* group) const;
+
   private:
     enum ControllerState {
         UNKNOWN = 0,