Replace last remaining NULLs in gfe/quic with nullptr. No behavior change.

net/quic/crypto/quic_crypto_server_config_test.cc

Index: net/quic/crypto/quic_crypto_server_config_test.cc
diff --git a/net/quic/crypto/quic_crypto_server_config_test.cc b/net/quic/crypto/quic_crypto_server_config_test.cc
index 21c338d94d46d19607daa2a30f7bc5239a782567..382d213cfa00bf4b86c78c3abc8e4dce5b3c62ac 100644
--- a/net/quic/crypto/quic_crypto_server_config_test.cc
+++ b/net/quic/crypto/quic_crypto_server_config_test.cc
@@ -277,14 +277,14 @@ class SourceAddressTokenTest : public ::testing::Test {
   }
 
   string NewSourceAddressToken(string config_id, const IPAddressNumber& ip) {
-    return NewSourceAddressToken(config_id, ip, NULL);
+    return NewSourceAddressToken(config_id, ip, nullptr);
   }
 
   string NewSourceAddressToken(string config_id,
                                const IPAddressNumber& ip,
                                const SourceAddressTokens& previous_tokens) {
     return peer_.NewSourceAddressToken(config_id, previous_tokens, ip, rand_,
-                                       clock_.WallNow(), NULL);
+                                       clock_.WallNow(), nullptr);
   }
 
   string NewSourceAddressToken(string config_id,
@@ -299,7 +299,7 @@ class SourceAddressTokenTest : public ::testing::Test {
       string config_id,
       StringPiece srct,
       const IPAddressNumber& ip) {
-    return ValidateSourceAddressTokens(config_id, srct, ip, NULL);
+    return ValidateSourceAddressTokens(config_id, srct, ip, nullptr);
   }
 
   HandshakeFailureReason ValidateSourceAddressTokens(