Add use_backup_ref_ptr gn args flag

Add use_backup_ref_ptr gn args flag which enables the ref count in PA and switches the CheckedPtr implementation to BackupRefPtr.

Also turns off backup ref ptr support for NaCl as it is compiled as 32bit but address_pool_manager is not available, causing a link errors.
https://source.chromium.org/chromium/chromium/src/+/master:base/BUILD.gn;l=1772

Bug: 1073933
Change-Id: I1e0ea1b1181623fa5783d39c6d9a379c1df2daf3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2626681Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843988}

base/BUILD.gn

@@ -70,6 +70,9 @@ declare_args() {
   # TODO(https://crbug.com/1149922): Remove this. If you're setting this to
   # false on a bot, please leave a note on that bug.
   build_base_unittests = true
+
+  # Set to true to use BackupRefPtr as the implementation of CheckedPtr.
+  use_backup_ref_ptr = false
 }
 
 # Mutex priority inheritance is disabled by default due to security
@@ -2336,7 +2339,10 @@ buildflag_header("partition_alloc_buildflags") {
   header = "partition_alloc_buildflags.h"
   header_dir = "base"
 
-  flags = [ "USE_PARTITION_ALLOC=$use_partition_alloc" ]
+  flags = [
+    "USE_PARTITION_ALLOC=$use_partition_alloc",
+    "USE_BACKUP_REF_PTR=$use_backup_ref_ptr",
+  ]
 }
 
 buildflag_header("clang_profiling_buildflags") {

base/allocator/partition_allocator/checked_ptr_support.h

@@ -5,8 +5,17 @@
 #ifndef BASE_ALLOCATOR_PARTITION_ALLOCATOR_CHECKED_PTR_SUPPORT_H_
 #define BASE_ALLOCATOR_PARTITION_ALLOCATOR_CHECKED_PTR_SUPPORT_H_
 
+#include "base/partition_alloc_buildflags.h"
+#include "build/build_config.h"
+#include "build/buildflag.h"
+
+#if BUILDFLAG(USE_BACKUP_REF_PTR) && !defined(OS_NACL)
+#define ENABLE_REF_COUNT_FOR_BACKUP_REF_PTR 1
+#define DISABLE_REF_COUNT_IN_RENDERER 1
+#else
 #define ENABLE_REF_COUNT_FOR_BACKUP_REF_PTR 0
 #define DISABLE_REF_COUNT_IN_RENDERER 0
+#endif
 
 #if DISABLE_REF_COUNT_IN_RENDERER
 static_assert(ENABLE_REF_COUNT_FOR_BACKUP_REF_PTR,

base/memory/checked_ptr.h

@@ -20,7 +20,12 @@
 #include "build/build_config.h"
 #include "build/buildflag.h"
 
+#if BUILDFLAG(USE_BACKUP_REF_PTR) && !defined(OS_NACL)
+#define ENABLE_BACKUP_REF_PTR_IMPL 1
+#else
 #define ENABLE_BACKUP_REF_PTR_IMPL 0
+#endif
+
 #if ENABLE_BACKUP_REF_PTR_IMPL
 static_assert(ENABLE_REF_COUNT_FOR_BACKUP_REF_PTR,
               "BackupRefPtrImpl can only by used if PartitionRefCount is "