Replace NULL with nullptr in all C++ files.

webrtc/modules/desktop_capture/screen_capturer_unittest.cc

Index: webrtc/modules/desktop_capture/screen_capturer_unittest.cc
diff --git a/webrtc/modules/desktop_capture/screen_capturer_unittest.cc b/webrtc/modules/desktop_capture/screen_capturer_unittest.cc
index 81ca87a8e41ea0c2195557dc3ae2b6e5af09c59d..9da1d1b4c6bdb539c5f9da7622fae20089eda624 100644
--- a/webrtc/modules/desktop_capture/screen_capturer_unittest.cc
+++ b/webrtc/modules/desktop_capture/screen_capturer_unittest.cc
@@ -128,7 +128,7 @@ TEST_F(ScreenCapturerTest, Capture) {
   EXPECT_GT(frame->size().height(), 0);
   EXPECT_GE(frame->stride(),
             frame->size().width() * DesktopFrame::kBytesPerPixel);
-  EXPECT_TRUE(frame->shared_memory() == NULL);
+  EXPECT_TRUE(frame->shared_memory() == nullptr);
 
   // Verify that the region contains whole screen.
   EXPECT_FALSE(frame->updated_region().is_empty());