[PA] Update comment for AllocNewSlotSpan

Missed in crrev.com/c/2741038

Change-Id: I6ff3e40ea100733dafc6c0ff203fe208cb10a228
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2744796
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#861022}

base/allocator/partition_allocator/partition_bucket.h

@@ -145,7 +145,7 @@ struct PartitionBucket {
   uint8_t get_system_pages_per_slot_span();
 
   // Allocates a new slot span with size |num_partition_pages| from the
-  // current extent. Metadata within this slot span will be uninitialized.
+  // current extent. Metadata within this slot span will be initialized.
   // Returns nullptr on error.
   ALWAYS_INLINE SlotSpanMetadata<thread_safe>* AllocNewSlotSpan(
       PartitionRoot<thread_safe>* root,