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.

tests/ceftests/test_server_unittest.cc

@@ -4,6 +4,7 @@
 
 #include <sstream>
 
+#include "include/base/cef_cxx17_backports.h"
 #include "include/cef_task.h"
 #include "include/cef_waitable_event.h"
 #include "include/wrapper/cef_closure_task.h"
@@ -237,7 +238,7 @@ TEST(TestServerTest, ObserverHelperMultiple) {
 
   TestState states[3];
   size_t count = 0;
-  const size_t size = arraysize(states);
+  const size_t size = base::size(states);
 
   const base::Closure& done_callback =
       base::Bind(SignalIfDone, event, base::Unretained(&count), size);