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/media_router_test.cc

@@ -74,7 +74,7 @@ class MediaRouteCreateCallback : public CefMediaRouteCreateCallback {
     } else {
       SendFailure(create_callback_, kRequestFailedError + result, error);
     }
-    create_callback_ = NULL;
+    create_callback_ = nullptr;
   }
 
  private:
@@ -257,7 +257,7 @@ class MediaObserver : public CefMediaObserver {
   CefRefPtr<CefMediaSource> GetSource(const std::string& source_urn) {
     CefRefPtr<CefMediaSource> source = media_router_->GetSource(source_urn);
     if (!source)
-      return NULL;
+      return nullptr;
     return source;
   }
 
@@ -265,7 +265,7 @@ class MediaObserver : public CefMediaObserver {
     SinkInfoMap::const_iterator it = sink_info_map_.find(sink_id);
     if (it != sink_info_map_.end())
       return it->second->sink;
-    return NULL;
+    return nullptr;
   }
 
   void ClearSinkInfoMap() {
@@ -299,7 +299,7 @@ class MediaObserver : public CefMediaObserver {
     RouteMap::const_iterator it = route_map_.find(route_id);
     if (it != route_map_.end())
       return it->second;
-    return NULL;
+    return nullptr;
   }
 
   void SendResponse(const std::string& name,
@@ -574,7 +574,7 @@ class Handler : public CefMessageRouterBrowserSide::Handler {
     if (it != subscription_state_map_.end()) {
       return it->second->observer;
     }
-    return NULL;
+    return nullptr;
   }
 
   // Map of browser ID to SubscriptionState object.