Blink: PCScan: Add runtime flag for PCScan only on WTF partitions

Bug: 11297512
Change-Id: I51a1de2a77553f2122ca01c62c1e5cb067c3b05f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2544893Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828809}

third_party/blink/renderer/platform/wtf/allocator/partitions.cc

@@ -46,6 +46,10 @@ namespace WTF {
 const char* const Partitions::kAllocatedObjectPoolName =
     "partition_alloc/allocated_objects";
 
+// Runs PCScan on WTF partitions.
+const base::Feature kPCScanBlinkPartitions{"PCScanBlinkPartitions",
+                                           base::FEATURE_DISABLED_BY_DEFAULT};
+
 bool Partitions::initialized_ = false;
 
 // These statics are inlined, so cannot be LazyInstances. We create the values,
@@ -99,7 +103,8 @@ bool Partitions::InitializeOnce() {
   buffer_root_ = buffer_allocator.root();
   layout_root_ = layout_allocator.root();
 
-  if (base::features::IsPartitionAllocPCScanEnabled()) {
+  if (base::features::IsPartitionAllocPCScanEnabled() ||
+      base::FeatureList::IsEnabled(kPCScanBlinkPartitions)) {
     fast_malloc_root_->EnablePCScan();
     buffer_root_->EnablePCScan();
     layout_root_->EnablePCScan();