[GPU-Plugin] Integration of a faster version of grow_gpu plugin into mainstream (#2360)

* Integrating a faster version of grow_gpu plugin
1. Removed the older files to reduce duplication
2. Moved all of the grow_gpu files under 'exact' folder
3. All of them are inside 'exact' namespace to avoid any conflicts
4. Fixed a bug in benchmark.py while running only 'grow_gpu' plugin
5. Added cub and googletest submodules to ease integration and unit-testing
6. Updates to CMakeLists.txt to directly build cuda objects into libxgboost

* Added support for building gpu plugins through make flow
1. updated makefile and config.mk to add right targets
2. added unit-tests for gpu exact plugin code

* 1. Added support for building gpu plugin using 'make' flow as well
2. Updated instructions for building and testing gpu plugin

* Fix travis-ci errors for PR#2360
1. lint errors on unit-tests
2. removed googletest, instead depended upon dmlc-core provide gtest cache

* Some more fixes to travis-ci lint failures PR#2360

* Added Rory's copyrights to the files containing code from both.

* updated copyright statement as per Rory's request

* moved the static datasets into a script to generate them at runtime

* 1. memory usage print when silent=0
2. tests/ and test/ folder organization
3. removal of the dependency of googletest for just building xgboost
4. coding style updates for .cuh as well

* Fixes for compilation warnings

* add cuda object files as well when JVM_BINDINGS=ON

plugin/updater_gpu/test/cpp/node.cu

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2017, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "gtest/gtest.h"
+#include "../../src/exact/node.cuh"
+
+
+namespace xgboost {
+namespace tree {
+namespace exact {
+
+TEST(Split, Test) {
+  Split s;
+  EXPECT_FALSE(s.isSplittable(0.5f));
+  s.score = 1.f;
+  EXPECT_FALSE(s.isSplittable(0.5f));
+  s.index = 2;
+  EXPECT_TRUE(s.isSplittable(0.5f));
+  EXPECT_FALSE(s.isSplittable(1.5f));
+}
+
+TEST(Node, Test) {
+  Node<int16_t> n;
+  EXPECT_TRUE(n.isUnused());
+  EXPECT_FALSE(n.isLeaf());
+  EXPECT_TRUE(n.isDefaultLeft());
+  n.dir = RightDir;
+  EXPECT_TRUE(n.isUnused());
+  EXPECT_FALSE(n.isLeaf());
+  EXPECT_FALSE(n.isDefaultLeft());
+  n.id = 123;
+  EXPECT_FALSE(n.isUnused());
+  EXPECT_TRUE(n.isLeaf());
+  EXPECT_FALSE(n.isDefaultLeft());
+  n.score = 0.5f;
+  EXPECT_FALSE(n.isUnused());
+  EXPECT_FALSE(n.isLeaf());
+  EXPECT_FALSE(n.isDefaultLeft());
+}
+
+TEST(Segment, Test) {
+  Segment s;
+  EXPECT_FALSE(s.isValid());
+  s.start = 2;
+  EXPECT_FALSE(s.isValid());
+  s.end = 4;
+  EXPECT_TRUE(s.isValid());
+}
+
+}  // namespace exact
+}  // namespace tree
+}  // namespace xgboost