Use folly/portability/GTest.h in folly/executurs/test/

Summary:
[Folly] Use `folly/portability/GTest.h` in `folly/executurs/test/`.

Applying the general rule for folly tests to some recently-introduced violations.

Reviewed By: Orvid

Differential Revision: D6113707

fbshipit-source-id: f9a2961ac845489b85b5a539595e4c82df03d922

folly/executors/task_queue/test/UnboundedBlockingQueueTest.cpp

@@ -15,7 +15,7 @@
  */
 #include <folly/executors/task_queue/UnboundedBlockingQueue.h>
 #include <folly/Baton.h>
-#include <gtest/gtest.h>
+#include <folly/portability/GTest.h>
 #include <thread>
 
 using namespace folly;

folly/executors/test/AsyncTest.cpp

@@ -16,7 +16,7 @@
 
 #include <folly/executors/Async.h>
 #include <folly/futures/ManualExecutor.h>
-#include <gtest/gtest.h>
+#include <folly/portability/GTest.h>
 
 using namespace folly;
 

folly/executors/test/CodelTest.cpp

@@ -15,7 +15,7 @@
  */
 
 #include <folly/executors/Codel.h>
-#include <gtest/gtest.h>
+#include <folly/portability/GTest.h>
 #include <chrono>
 #include <thread>
 

folly/executors/test/GlobalExecutorTest.cpp

@@ -16,7 +16,7 @@
 
 #include <folly/executors/GlobalExecutor.h>
 #include <folly/executors/IOExecutor.h>
-#include <gtest/gtest.h>
+#include <folly/portability/GTest.h>
 
 using namespace folly;
 

folly/executors/test/SerialExecutorTest.cpp

@@ -16,12 +16,11 @@
 
 #include <chrono>
 
-#include <gtest/gtest.h>
-
 #include <folly/Baton.h>
 #include <folly/executors/CPUThreadPoolExecutor.h>
 #include <folly/executors/SerialExecutor.h>
 #include <folly/futures/InlineExecutor.h>
+#include <folly/portability/GTest.h>
 
 using namespace std::chrono;
 using folly::SerialExecutor;

folly/executors/test/ThreadPoolExecutorTest.cpp

@@ -22,7 +22,7 @@
 #include <folly/executors/ThreadPoolExecutor.h>
 #include <folly/executors/task_queue/LifoSemMPMCQueue.h>
 #include <folly/executors/thread_factory/PriorityThreadFactory.h>
-#include <gtest/gtest.h>
+#include <folly/portability/GTest.h>
 
 using namespace folly;
 using namespace std::chrono;

folly/executors/test/ThreadedExecutorTest.cpp

@@ -16,11 +16,10 @@
 
 #include <folly/executors/ThreadedExecutor.h>
 
-#include <gtest/gtest.h>
-
 #include <folly/Conv.h>
 #include <folly/futures/Future.h>
 #include <folly/gen/Base.h>
+#include <folly/portability/GTest.h>
 
 namespace {