Disable base::{Once,Repeating}Callback construction from nullptr

A constructor of base::{Once,Repeating}Callback takes a pointer to
BindStateBase, that is intended to be used by base::Bind*.
However, the constructor accidentally matches to nullptr parameter, and
that requires a null check of |bind_state| in the callback constructor.

This CL disables nullptr argument on the callback construction.

Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ic74ca7ce94bc95922e122257d397ff5fbf1fa431
Reviewed-on: https://chromium-review.googlesource.com/1111179
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569782}

base/callback.h

@@ -8,6 +8,8 @@
 #ifndef BASE_CALLBACK_H_
 #define BASE_CALLBACK_H_
 
+#include <stddef.h>
+
 #include "base/callback_forward.h"
 #include "base/callback_internal.h"
 
@@ -58,6 +60,7 @@ class OnceCallback<R(Args...)> : public internal::CallbackBase {
                                   internal::PassingTraitsType<Args>...);
 
   constexpr OnceCallback() = default;
+  OnceCallback(std::nullptr_t) = delete;
 
   explicit OnceCallback(internal::BindStateBase* bind_state)
       : internal::CallbackBase(bind_state) {}
@@ -105,6 +108,7 @@ class RepeatingCallback<R(Args...)> : public internal::CallbackBaseCopyable {
                                   internal::PassingTraitsType<Args>...);
 
   constexpr RepeatingCallback() = default;
+  RepeatingCallback(std::nullptr_t) = delete;
 
   explicit RepeatingCallback(internal::BindStateBase* bind_state)
       : internal::CallbackBaseCopyable(bind_state) {}

components/safe_browsing/browser/threat_details.cc

@@ -355,7 +355,6 @@ ThreatDetails::ThreatDetails()
       num_visits_(0),
       ambiguous_dom_(false),
       trim_to_ad_tags_(false),
-      done_callback_(nullptr),
       all_done_expected_(false),
       is_all_done_(false) {}
 

ios/web/app/web_main.mm

@@ -16,7 +16,6 @@ WebMainParams::WebMainParams() : WebMainParams(nullptr) {}
 WebMainParams::WebMainParams(WebMainDelegate* delegate)
     : delegate(delegate),
       register_exit_manager(true),
-      get_task_scheduler_init_params_callback(nullptr),
       argc(0),
       argv(nullptr) {}