Reapply "libprocessgroup: Combine all 3 ActivateControllers imple..."

This reverts commit 0fa49253a484fc0c99d067ade57a4978059b3a95.

Change-Id: I83121ff295caaabc0a2fd8a606ee2d52dacb0174
diff --git a/libprocessgroup/cgroup_map.h b/libprocessgroup/cgroup_map.h
index 5ad59bd..fb99076 100644
--- a/libprocessgroup/cgroup_map.h
+++ b/libprocessgroup/cgroup_map.h
@@ -58,7 +58,7 @@
     static CgroupMap& GetInstance();
     CgroupControllerWrapper FindController(const std::string& name) const;
     CgroupControllerWrapper FindControllerByPath(const std::string& path) const;
-    int ActivateControllers(const std::string& path) const;
+    bool ActivateControllers(const std::string& path) const;
 
   private:
     bool loaded_ = false;