Fix ios-simulator-cronet build failure

Move the problematic include under the ENABLE_BACKUP_REF_PTR_IMPL flag.

Change-Id: I15340b867bb51fda4894ea260bdd8ac59f666e1d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2595369
Auto-Submit: Sergei Glazunov <glazunov@google.com>
Reviewed-by: Benoit L <lizeb@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837679}

base/memory/checked_ptr.cc

@@ -4,14 +4,14 @@
 
 #include "base/memory/checked_ptr.h"
 
+#if ENABLE_BACKUP_REF_PTR_IMPL
+
 #include "base/allocator/partition_allocator/partition_alloc.h"
 
 namespace base {
 
 namespace internal {
 
-#if ENABLE_BACKUP_REF_PTR_IMPL
-
 void BackupRefPtrImpl::AcquireInternal(void* ptr) {
   void* slot_start = PartitionAllocGetSlotStart(ptr);
   PartitionRefCountPointer(slot_start)->Acquire();
@@ -28,8 +28,8 @@ bool BackupRefPtrImpl::IsPointeeAlive(void* ptr) {
   return PartitionRefCountPointer(slot_start)->IsAlive();
 }
 
-#endif  // ENABLE_BACKUP_REF_PTR_IMPL
-
 }  // namespace internal
 
 }  // namespace base
+
+#endif  // ENABLE_BACKUP_REF_PTR_IMPL