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/osr_accessibility_node.cc

@@ -97,7 +97,7 @@ void OsrAXNode::UpdateValue(CefRefPtr<CefDictionaryValue> value) {
 CefWindowHandle OsrAXNode::GetWindowHandle() const {
   if (accessibility_helper_)
     return accessibility_helper_->GetWindowHandle();
-  return NULL;
+  return nullptr;
 }
 
 CefRefPtr<CefBrowser> OsrAXNode::GetBrowser() const {