memory_pool: Deduplicate slab allocation code (#28)

src/common/memory_pool.h

@@ -28,6 +28,11 @@ public:
     void* Alloc();
 
 private:
+    // Allocates a completely new memory slab.
+    // Used when an entirely new slab is needed
+    // due the current one running out of usable space.
+    void AllocateNewSlab();
+
     size_t object_size;
     size_t slab_size;
     char* current_slab;