Make AlignedAllocations test use aligned root

This is a continuation of crrev.com/c/2275886. If PA-Everywhere and
tagging for CheckedPtr were to be enabled, this test would've failed.
By switching to aligned root, we're making it pass in all situations.

Bug: 1092288, 998048
Change-Id: Ib638818cc1e433c937c3c6fd375a492f5b3b22ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2282837
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786170}

base/allocator/partition_allocator/partition_alloc.h

@@ -900,6 +900,19 @@ ALWAYS_INLINE size_t PartitionRoot<thread_safe>::ActualSize(size_t size) {
 #endif
 }
 
+enum class PartitionAllocatorAlignment {
+  // By default all allocations will be aligned to 8B (16B if
+  // BUILDFLAG_INTERNAL_USE_PARTITION_ALLOC_AS_MALLOC is true).
+  kRegular,
+
+  // In addition to the above alignment enforcement, this option allows using
+  // AlignedAlloc() which can align at a larger boundary.
+  // This option comes at a cost of disallowing cookies on Debug builds and tags
+  // for CheckedPtr. It also causes all allocations to go outside of GigaCage,
+  // so that CheckedPtr can easily tell if a pointer comes with a tag or not.
+  kAlignedAlloc,
+};
+
 namespace internal {
 template <bool thread_safe>
 struct BASE_EXPORT PartitionAllocator {
@@ -909,8 +922,9 @@ struct BASE_EXPORT PartitionAllocator {
         &partition_root_);
   }
 
-  void init() {
-    partition_root_.Init(true);
+  void init(PartitionAllocatorAlignment alignment =
+                PartitionAllocatorAlignment::kRegular) {
+    partition_root_.Init(alignment == PartitionAllocatorAlignment::kRegular);
     PartitionAllocMemoryReclaimer::Instance()->RegisterPartition(
         &partition_root_);
   }

base/allocator/partition_allocator/partition_alloc_unittest.cc

@@ -150,7 +150,8 @@ class PartitionAllocTest : public testing::Test {
   void SetUp() override {
     scoped_feature_list.InitWithFeatures({kPartitionAllocGigaCage}, {});
     PartitionAllocGlobalInit(HandleOOM);
-    allocator.init();
+    allocator.init(PartitionAllocatorAlignment::kRegular);
+    aligned_allocator.init(PartitionAllocatorAlignment::kAlignedAlloc);
     test_bucket_index_ = SizeToIndex(kRealAllocSize);
   }
 
@@ -290,6 +291,7 @@ class PartitionAllocTest : public testing::Test {
 
   base::test::ScopedFeatureList scoped_feature_list;
   PartitionAllocator<base::internal::ThreadSafe> allocator;
+  PartitionAllocator<base::internal::ThreadSafe> aligned_allocator;
   size_t test_bucket_index_;
 };
 
@@ -2448,7 +2450,7 @@ TEST_F(PartitionAllocTest, AlignedAllocations) {
 
   for (size_t alloc_size : alloc_sizes) {
     for (size_t alignment : alignemnts) {
-      void* ptr = allocator.root()->AlignedAlloc(alignment, alloc_size);
+      void* ptr = aligned_allocator.root()->AlignedAlloc(alignment, alloc_size);
       ASSERT_TRUE(ptr);
       EXPECT_EQ(reinterpret_cast<uintptr_t>(ptr) % alignment, 0ull);
       allocator.root()->Free(ptr);