PA: Opt V8 partitions into "small" sss

These were already successfully launched in the PA-E and Blink
partitions. We anticipate no performance hit in enabling them here.

Bug: 333443437
Change-Id: I73eb08d784816aa81dbed4e6844bf56b03dbc967
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6275837
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Kalvin Lee <kdlee@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1423006}

gin/array_buffer.cc

@@ -90,6 +90,11 @@ void ArrayBufferAllocator::InitializePartition() {
   // freelist impl selection to a compile-time seam.
   opts.use_pool_offset_freelists = partition_alloc::PartitionOptions::kEnabled;
 
+  // TODO(crbug.com/333443437): Remove this user-configurable toggle and
+  // default all buckets to "small" single-slot spans.
+  opts.use_small_single_slot_spans =
+      partition_alloc::PartitionOptions::kEnabled;
+
   static base::NoDestructor<partition_alloc::PartitionAllocator>
       partition_allocator(opts);
 

gin/v8_platform_thread_isolated_allocator.cc

@@ -34,6 +34,11 @@ void ThreadIsolatedAllocator::Initialize(int pkey) {
   // freelist impl selection to a compile-time seam.
   opts.use_pool_offset_freelists = partition_alloc::PartitionOptions::kEnabled;
 
+  // TODO(crbug.com/333443437): Remove this user-configurable toggle and
+  // default all buckets to "small" single-slot spans.
+  opts.use_small_single_slot_spans =
+      partition_alloc::PartitionOptions::kEnabled;
+
   allocator_.init(opts);
 }