Various fixes related to the C++11/14 update (see issue #3140)

- Convert scoped_ptr to std::unique_ptr from <memory>
- Convert arraysize to base::size from include/base/cef_cxx17_backports.h
- Convert NULL to nullptr
- Include include/base/cef_callback.h instead of include/base/cef_bind.h
- Implicit conversion of CefRefPtr<T> or scoped_refptr<T> to T* is gone;
  use .get() instead

See the issue for additional details.

libcef_dll/shutdown_checker.cc

@@ -4,13 +4,7 @@
 
 #include "libcef_dll/shutdown_checker.h"
 
-// For compatibility with older client compiler versions only use std::atomic
-// on the library side.
-#if defined(BUILDING_CEF_SHARED)
 #include <atomic>
-#else
-#include "include/base/cef_atomic_ref_count.h"
-#endif
 
 #include "include/base/cef_logging.h"
 
@@ -20,8 +14,6 @@ namespace shutdown_checker {
 
 namespace {
 
-#if defined(BUILDING_CEF_SHARED)
-
 std::atomic_bool g_cef_shutdown{false};
 
 bool IsCefShutdown() {
@@ -32,20 +24,6 @@ void SetCefShutdown() {
   g_cef_shutdown.store(true);
 }
 
-#else  // !defined(BUILDING_CEF_SHARED)
-
-base::AtomicRefCount g_cef_shutdown ATOMIC_DECLARATION;
-
-bool IsCefShutdown() {
-  return !base::AtomicRefCountIsZero(&g_cef_shutdown);
-}
-
-void SetCefShutdown() {
-  base::AtomicRefCountInc(&g_cef_shutdown);
-}
-
-#endif  // !defined(BUILDING_CEF_SHARED)
-
 }  // namespace
 
 void AssertNotShutdown() {