Use DART tree weights when computing SHAPs (#5050)

This PR fixes tree weights in dart being ignored when computing contributions.

* Fix ellpack page source link.
* Add tree weights to compute contribution.

src/data/ellpack_page.cc

@@ -10,6 +10,8 @@ namespace xgboost {
 
 class EllpackPageImpl {};
 
+EllpackPage::EllpackPage() = default;
+
 EllpackPage::EllpackPage(DMatrix* dmat, const BatchParam& param) {
   LOG(FATAL) << "Internal Error: XGBoost is not compiled with CUDA but EllpackPage is required";
 }

src/data/ellpack_page_source.cc

@@ -3,8 +3,8 @@
  */
 #ifndef XGBOOST_USE_CUDA
 
+#include <xgboost/data.h>
 #include "ellpack_page_source.h"
-
 namespace xgboost {
 namespace data {
 

src/data/ellpack_page_source.cu

@@ -1,14 +1,14 @@
 /*!
  * Copyright 2019 XGBoost contributors
  */
-
-#include "ellpack_page_source.h"
-
 #include <memory>
 #include <utility>
 #include <vector>
 
 #include "../common/hist_util.h"
+
+#include "ellpack_page_source.h"
+#include "sparse_page_source.h"
 #include "ellpack_page.cuh"
 
 namespace xgboost {

src/data/ellpack_page_source.h

@@ -9,7 +9,6 @@
 #include <memory>
 #include <string>
 
-#include "sparse_page_source.h"
 #include "../common/timer.h"
 
 namespace xgboost {