Replace NULL with nullptr in all C++ files.

webrtc/tools/frame_editing/frame_editing_unittest.cc

Index: webrtc/tools/frame_editing/frame_editing_unittest.cc
diff --git a/webrtc/tools/frame_editing/frame_editing_unittest.cc b/webrtc/tools/frame_editing/frame_editing_unittest.cc
index d61ec00bd78009e85cd6f6b6a1af09d52264a12b..01843e8df5451eb2177360bc9d103643dcacfd84 100644
--- a/webrtc/tools/frame_editing/frame_editing_unittest.cc
+++ b/webrtc/tools/frame_editing/frame_editing_unittest.cc
@@ -34,7 +34,7 @@ class FrameEditingTest : public ::testing::Test {
                                              "frame_editing_unittest.yuv");
 
     original_fid_ = fopen(reference_video_.c_str(), "rb");
-    ASSERT_TRUE(original_fid_ != NULL);
+    ASSERT_TRUE(original_fid_ != nullptr);
 
     // Ensure the output file exists on disk.
     std::ofstream(test_video_.c_str(), std::ios::out);
@@ -42,7 +42,7 @@ class FrameEditingTest : public ::testing::Test {
     // TODO(holmer): Figure out why this file has to be opened here (test fails
     // if it's opened after the write operation performed in EditFrames).
     edited_fid_ = fopen(test_video_.c_str(), "rb");
-    ASSERT_TRUE(edited_fid_ != NULL);
+    ASSERT_TRUE(edited_fid_ != nullptr);
 
     original_buffer_.reset(new int[kFrameSize]);
     edited_buffer_.reset(new int[kFrameSize]);