PartitionAlloc: Encapsulate giga-cage checks in a per-root function.

This is to make it less error prone if checks are augmented in one
place but not in the other.

Bug: 11297512
Change-Id: Id5518f703bf7240f8634570996eb5ec4eda10f94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2471332
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Takashi Sakamoto <tasak@google.com>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819314}

base/allocator/partition_allocator/partition_bucket.cc

@@ -50,7 +50,7 @@ PartitionDirectMap(PartitionRoot<thread_safe>* root, int flags, size_t raw_size)
   // Allocate from GigaCage, if enabled. However, the exception to this is when
   // tags aren't allowed, as CheckedPtr assumes that everything inside GigaCage
   // uses tags (specifically, inside the GigaCage's normal bucket pool).
-  if (root->allow_extras && features::IsPartitionAllocGigaCageEnabled()) {
+  if (root->UsesGigaCage()) {
     ptr = internal::AddressPoolManager::GetInstance()->Alloc(GetDirectMapPool(),
                                                              nullptr, map_size);
   } else {

base/allocator/partition_allocator/partition_root.h

@@ -6,6 +6,7 @@
 #define BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ROOT_H_
 
 #include "base/allocator/partition_allocator/partition_alloc_constants.h"
+#include "base/allocator/partition_allocator/partition_alloc_features.h"
 #include "base/allocator/partition_allocator/partition_alloc_forward.h"
 #include "base/allocator/partition_allocator/partition_direct_map_extent.h"
 #include "base/allocator/partition_allocator/partition_lock.h"
@@ -220,6 +221,10 @@ struct BASE_EXPORT PartitionRoot {
 #endif
   }
 
+  bool UsesGigaCage() const {
+    return features::IsPartitionAllocGigaCageEnabled() && allow_extras;
+  }
+
  private:
   // Allocates memory, without initializing extras.
   //

base/allocator/partition_allocator/pcscan.cc

@@ -237,7 +237,7 @@ size_t NO_SANITIZE("thread") PCScan<thread_safe>::PCScanTask::ScanPartition() {
 #if defined(PA_HAS_64_BITS_POINTERS)
       // On partitions without extras (partitions with aligned allocations),
       // memory is not allocated from the GigaCage.
-      if (features::IsPartitionAllocGigaCageEnabled() && root_.allow_extras) {
+      if (root_.UsesGigaCage()) {
         // With GigaCage, we first do a fast bitmask check to see if the pointer
         // points to the normal bucket pool.
         if (!PartitionAddressSpace::IsInNormalBucketPool(