Mojo: NULL -> nullptr in mojo/system and mojo/embedder.

mojo/system/raw_channel_posix.cc

Index: mojo/system/raw_channel_posix.cc
diff --git a/mojo/system/raw_channel_posix.cc b/mojo/system/raw_channel_posix.cc
index 01453f63be4845c8dfb227772b14a59d3fb53450..6ee85945df0522c7306c5a1952bf880184a105b0 100644
--- a/mojo/system/raw_channel_posix.cc
+++ b/mojo/system/raw_channel_posix.cc
@@ -138,7 +138,7 @@ void RawChannelPosix::EnqueueMessageNoLock(
             MessageInTransit::kTypeRawChannel,
             MessageInTransit::kSubtypeRawChannelPosixExtraPlatformHandles,
             0,
-            NULL));
+            nullptr));
         embedder::ScopedPlatformHandleVectorPtr fds(
             new embedder::PlatformHandleVector(
                 platform_handles->begin() + i,
@@ -405,7 +405,7 @@ void RawChannelPosix::OnFileCanWriteWithoutBlocking(int fd) {
 }
 
 RawChannel::IOResult RawChannelPosix::ReadImpl(size_t* bytes_read) {
-  char* buffer = NULL;
+  char* buffer = nullptr;
   size_t bytes_to_read = 0;
   read_buffer()->GetBuffer(&buffer, &bytes_to_read);