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/cefclient/browser/main_context_impl_win.cc

@@ -14,8 +14,8 @@ std::string MainContextImpl::GetDownloadPath(const std::string& file_name) {
   std::string path;
 
   // Save the file in the user's "My Documents" folder.
-  if (SUCCEEDED(SHGetFolderPath(NULL, CSIDL_PERSONAL | CSIDL_FLAG_CREATE, NULL,
-                                0, szFolderPath))) {
+  if (SUCCEEDED(SHGetFolderPath(nullptr, CSIDL_PERSONAL | CSIDL_FLAG_CREATE,
+                                nullptr, 0, szFolderPath))) {
     path = CefString(szFolderPath);
     path += "\\" + file_name;
   }