Allow BackupRefPtr on 32-bit

The |defined(ARCH_CPU_64_BITS)| check is a remnant of the
CheckedPtr2/MTECheckedPtr era, which worked only with 64-bit pointers.
BackupRefPtr doesn't have this limitation.

Bug: 1073933
Change-Id: I8e3dc79291b6bd2b118cb34b0b564f58e4ccc785
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2571143
Auto-Submit: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837917}

base/memory/checked_ptr.h

@@ -100,8 +100,6 @@ struct CheckedPtrNoOpImpl {
   static ALWAYS_INLINE void IncrementSwapCountForTest() {}
 };
 
-#if defined(ARCH_CPU_64_BITS) && !defined(OS_NACL)
-
 #if ENABLE_BACKUP_REF_PTR_IMPL
 
 struct BackupRefPtrImpl {
@@ -204,8 +202,6 @@ struct BackupRefPtrImpl {
 
 #endif  // ENABLE_BACKUP_REF_PTR_IMPL
 
-#endif  // defined(ARCH_CPU_64_BITS) && !defined(OS_NACL)
-
 }  // namespace internal
 
 // DO NOT USE! EXPERIMENTAL ONLY! This is helpful for local testing!
@@ -223,15 +219,13 @@ struct BackupRefPtrImpl {
 //    we aren't striving to maximize compatibility with raw pointers, merely
 //    adding support for cases encountered so far).
 template <typename T,
-#if defined(ARCH_CPU_64_BITS) && !defined(OS_NACL) && \
-    BUILDFLAG(USE_PARTITION_ALLOC)
+#if BUILDFLAG(USE_PARTITION_ALLOC)
 #if ENABLE_BACKUP_REF_PTR_IMPL
           typename Impl = internal::BackupRefPtrImpl>
 #else
           typename Impl = internal::CheckedPtrNoOpImpl>
 #endif
-#else  // defined(ARCH_CPU_64_BITS) && !defined(OS_NACL) &&
-       // BUILDFLAG(USE_PARTITION_ALLOC)
+#else  // BUILDFLAG(USE_PARTITION_ALLOC)
           typename Impl = internal::CheckedPtrNoOpImpl>
 #endif
 class CheckedPtr {

base/memory/checked_ptr_unittest.cc

@@ -705,8 +705,6 @@ TEST_F(CheckedPtrTest, AssignmentFromNullptr) {
 
 }  // namespace
 
-#if defined(ARCH_CPU_64_BITS) && !defined(OS_NACL)
-
 namespace base {
 namespace internal {
 
@@ -760,5 +758,3 @@ TEST(BackupRefPtrImpl, Basic) {
         // !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
 }  // namespace internal
 }  // namespace base
-
-#endif  // defined(ARCH_CPU_64_BITS) && !defined(OS_NACL)