Revert "[PartitionAlloc] Temporarily use CHECK in SetFreelistHead"

This reverts commit 77307244.

Reason for revert: collected crash dumps so we can turn it back to DCHECK

Original change's description:
> [PartitionAlloc] Temporarily use CHECK in SetFreelistHead
>
> Temporarily use CHECK in SetFreelistHead to debug a crash.
> Should be reverted after a Canary release.
>
> Bug: 1137799
> Change-Id: I9e01a5cdfafb7da2af76997f8c42716394ac4cd3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2491724
> Reviewed-by: Benoit L <lizeb@chromium.org>
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
> Commit-Queue: Keishi Hattori <keishi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#819797}

TBR=yukishiino@chromium.org,tasak@google.com,haraken@chromium.org,keishi@chromium.org,lizeb@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1137799
Change-Id: I645119e34f6767b9e6a6d1fc739efb0e2c85aff5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500387Reviewed-by: Keishi Hattori <keishi@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821094}

base/allocator/partition_allocator/partition_page.h

@@ -365,9 +365,9 @@ ALWAYS_INLINE size_t SlotSpanMetadata<thread_safe>::GetRawSize() const {
 template <bool thread_safe>
 ALWAYS_INLINE void SlotSpanMetadata<thread_safe>::SetFreelistHead(
     PartitionFreelistEntry* new_head) {
-  PA_CHECK(!new_head ||
-           (reinterpret_cast<uintptr_t>(this) & kSuperPageBaseMask) ==
-               (reinterpret_cast<uintptr_t>(new_head) & kSuperPageBaseMask));
+  PA_DCHECK(!new_head ||
+            (reinterpret_cast<uintptr_t>(this) & kSuperPageBaseMask) ==
+                (reinterpret_cast<uintptr_t>(new_head) & kSuperPageBaseMask));
   freelist_head = new_head;
 }