[ObjC ARC] Converts ios/chrome/browser/ui/bookmarks:bookmarks to ARC.

ios/chrome/browser/ui/bookmarks/bookmark_position_cache.mm

Index: ios/chrome/browser/ui/bookmarks/bookmark_position_cache.mm
diff --git a/ios/chrome/browser/ui/bookmarks/bookmark_position_cache.mm b/ios/chrome/browser/ui/bookmarks/bookmark_position_cache.mm
index 51fdd984947bca708c8769efe112f4ecde131e14..2d3372ecf8b97e256ce4a71d9e0e27eb1a06b2a6 100644
--- a/ios/chrome/browser/ui/bookmarks/bookmark_position_cache.mm
+++ b/ios/chrome/browser/ui/bookmarks/bookmark_position_cache.mm
@@ -7,7 +7,6 @@
 #include <stdint.h>
 
 #include "base/logging.h"
-#include "base/mac/objc_property_releaser.h"
 
 namespace {
 // The current version of the cached position. This number should be incremented
@@ -45,10 +44,10 @@ NSString* kVersionKey = @"VersionKey";
 
 + (BookmarkPositionCache*)cacheForMenuItemFolderWithPosition:(CGFloat)position
                                                     folderId:(int64_t)folderId {
-  return [[[BookmarkPositionCache alloc]
+  return [[BookmarkPositionCache alloc]
       initWithFolderId:folderId
               position:position
-                  type:bookmarks::MenuItemFolder] autorelease];
+                  type:bookmarks::MenuItemFolder];
 }
 
 #pragma mark - Designated Initializer
@@ -103,17 +102,14 @@ NSString* kVersionKey = @"VersionKey";
   int typeInt = [coder decodeIntForKey:kTypeKey];
 
   if (version != kVersion) {
-    [self release];
     return nil;
   }
 
   if (!bookmarks::NumberIsValidMenuItemType(typeInt)) {
-    [self release];
     return nil;
   }
 
   if (typeInt == kMenuItemManaged) {
-    [self release];
     return nil;
   }