Rename flag --quic_export_server_num_packets_per_write_histogram to --quic_export_write_path_stats_at_server.

I plan to add a couple of histograms under the same flag.

PiperOrigin-RevId: 339311828
Change-Id: Icf2f912914d05841e08637c1c697391b89bec08a

quic/core/quic_packet_creator.cc

diff --git a/quic/core/quic_packet_creator.cc b/quic/core/quic_packet_creator.cc
index 662754e..3db37ed 100644
--- a/quic/core/quic_packet_creator.cc
+++ b/quic/core/quic_packet_creator.cc
@@ -1464,7 +1464,7 @@
   FlushCurrentPacket();
   SendRemainingPendingPadding();
   flusher_attached_ = false;
-  if (GetQuicFlag(FLAGS_quic_export_server_num_packets_per_write_histogram)) {
+  if (GetQuicFlag(FLAGS_quic_export_write_path_stats_at_server)) {
     if (!write_start_packet_number_.IsInitialized()) {
       QUIC_BUG << "write_start_packet_number is not initialized";
       return;

quic/core/quic_protocol_flags_list.h

diff --git a/quic/core/quic_protocol_flags_list.h b/quic/core/quic_protocol_flags_list.h
index 2509240..c39d1e0 100644
--- a/quic/core/quic_protocol_flags_list.h
+++ b/quic/core/quic_protocol_flags_list.h
@@ -88,11 +88,10 @@
     0.125f,  // One-eighth smoothed RTT
     "Smoothed RTT fraction that a connection can pace packets into the future.")
 
-QUIC_PROTOCOL_FLAG(
-    bool,
-    quic_export_server_num_packets_per_write_histogram,
-    false,
-    "If true, export number of packets written per write operation histogram.")
+QUIC_PROTOCOL_FLAG(bool,
+                   quic_export_write_path_stats_at_server,
+                   false,
+                   "If true, export detailed write path statistics at server.")
 
 QUIC_PROTOCOL_FLAG(bool,
                    quic_disable_version_negotiation_grease_randomness,