Run clang-tidy modernize-use-nullptr on //net

An instance of GetAddressOf() in url_security_manager_win.cc has also been updated to allow presubmit checks to pass.

This is a mechanical change.
See bugs for justification and details.

Bug: 776257, 778942
Change-Id: Ia8bb79e611be7a884227852224623043af8b850e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1512637
Reviewed-by: Bence Béky <[email protected]>
Reviewed-by: Matt Menke <[email protected]>
Commit-Queue: Raul Tambre <[email protected]>
Cr-Commit-Position: refs/heads/master@{#639546}
diff --git a/net/dns/record_parsed.h b/net/dns/record_parsed.h
index be227d4..27d771d 100644
--- a/net/dns/record_parsed.h
+++ b/net/dns/record_parsed.h
@@ -38,7 +38,7 @@
 
   template <class T> const T* rdata() const {
     if (T::kType != type_)
-      return NULL;
+      return nullptr;
     return static_cast<const T*>(rdata_.get());
   }