Replace NULL with nullptr in all C++ files.

webrtc/test/frame_generator_capturer.cc

Index: webrtc/test/frame_generator_capturer.cc
diff --git a/webrtc/test/frame_generator_capturer.cc b/webrtc/test/frame_generator_capturer.cc
index 65be9562c58a100339cd18693f55c00458d09654..97a5b2e71aba02bd2c74f0184e155921bf5a1db0 100644
--- a/webrtc/test/frame_generator_capturer.cc
+++ b/webrtc/test/frame_generator_capturer.cc
@@ -29,7 +29,7 @@ FrameGeneratorCapturer* FrameGeneratorCapturer::Create(size_t width,
       clock, FrameGenerator::CreateChromaGenerator(width, height), target_fps);
   if (!capturer->Init()) {
     delete capturer;
-    return NULL;
+    return nullptr;
   }
 
   return capturer;
@@ -47,7 +47,7 @@ FrameGeneratorCapturer* FrameGeneratorCapturer::CreateFromYuvFile(
       target_fps);
   if (!capturer->Init()) {
     delete capturer;
-    return NULL;
+    return nullptr;
   }
 
   return capturer;
@@ -83,7 +83,7 @@ void FrameGeneratorCapturer::SetFakeRotation(VideoRotation rotation) {
 bool FrameGeneratorCapturer::Init() {
   // This check is added because frame_generator_ might be file based and should
   // not crash because a file moved.
-  if (frame_generator_.get() == NULL)
+  if (frame_generator_.get() == nullptr)
     return false;
 
   if (!tick_->StartTimer(true, 1000 / target_fps_))