Convert Pass()→std::move() for iOS build.

ios/net/http_cache_helper.cc

Index: ios/net/http_cache_helper.cc
diff --git a/ios/net/http_cache_helper.cc b/ios/net/http_cache_helper.cc
index 4e67b988d1fdc74a6b1e5c877a631ceaa566641e..1702cace9014152953903b6545c6d084709fe827 100644
--- a/ios/net/http_cache_helper.cc
+++ b/ios/net/http_cache_helper.cc
@@ -4,6 +4,8 @@
 
 #include "ios/net/http_cache_helper.h"
 
+#include <utility>
+
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
@@ -67,7 +69,7 @@ void ClearHttpCacheOnIOThread(
   scoped_ptr<disk_cache::Backend*> backend(new disk_cache::Backend*(nullptr));
   disk_cache::Backend** backend_ptr = backend.get();
   net::CompletionCallback doom_callback =
-      base::Bind(&DoomHttpCache, base::Passed(backend.Pass()),
+      base::Bind(&DoomHttpCache, base::Passed(std::move(backend)),
                  client_task_runner, callback);
 
   int rv = http_cache->GetBackend(backend_ptr, doom_callback);