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/browser/browser_platform_delegate.h

@@ -356,7 +356,7 @@ class CefBrowserPlatformDelegate {
   virtual void StopFinding(bool clearSelection);
 
  protected:
-  // Allow deletion via scoped_ptr only.
+  // Allow deletion via std::unique_ptr only.
   friend std::default_delete<CefBrowserPlatformDelegate>;
 
   CefBrowserPlatformDelegate();