HttpServerProperties - Don't persist if ClearAlternativeService is

called with the same origin (HostPortPair) and nothing was deleted.

This change reduces the number of times ClearAlternativeService tries to
persist HttpServerProperties to disk (currently ~11% of persist calls
are due to ClearAlternativeService).

BUG=451256
R=rch@chromium.org

Review URL: https://codereview.chromium.org/1156513004

Cr-Commit-Position: refs/heads/master@{#333147}

net/http/http_server_properties_manager.cc

@@ -252,8 +252,14 @@ void HttpServerPropertiesManager::ConfirmAlternativeService(
 void HttpServerPropertiesManager::ClearAlternativeService(
     const HostPortPair& origin) {
   DCHECK(network_task_runner_->RunsTasksOnCurrentThread());
+  const AlternativeServiceMap& map =
+      http_server_properties_impl_->alternative_service_map();
+  size_t old_size = map.size();
   http_server_properties_impl_->ClearAlternativeService(origin);
-  ScheduleUpdatePrefsOnNetworkThread(CLEAR_ALTERNATIVE_SERVICE);
+  size_t new_size = map.size();
+  // Persist only if we have deleted an entry.
+  if (old_size != new_size)
+    ScheduleUpdatePrefsOnNetworkThread(CLEAR_ALTERNATIVE_SERVICE);
 }
 
 const AlternativeServiceMap&

net/http/http_server_properties_manager_unittest.cc

@@ -528,6 +528,27 @@ TEST_F(HttpServerPropertiesManagerTest, GetAlternativeService) {
   EXPECT_EQ(NPN_SPDY_4, alternative_service.protocol);
 }
 
+TEST_F(HttpServerPropertiesManagerTest, ClearAlternativeService) {
+  ExpectPrefsUpdate();
+  ExpectScheduleUpdatePrefsOnNetworkThread();
+
+  HostPortPair spdy_server_mail("mail.google.com", 80);
+  EXPECT_FALSE(HasAlternativeService(spdy_server_mail));
+  AlternativeService alternative_service(NPN_SPDY_4, "mail.google.com", 443);
+  http_server_props_manager_->SetAlternativeService(spdy_server_mail,
+                                                    alternative_service, 1.0);
+  ExpectScheduleUpdatePrefsOnNetworkThread();
+  http_server_props_manager_->ClearAlternativeService(spdy_server_mail);
+  // ExpectScheduleUpdatePrefsOnNetworkThread() should be called only once.
+  http_server_props_manager_->ClearAlternativeService(spdy_server_mail);
+
+  // Run the task.
+  base::RunLoop().RunUntilIdle();
+  Mock::VerifyAndClearExpectations(http_server_props_manager_.get());
+
+  EXPECT_FALSE(HasAlternativeService(spdy_server_mail));
+}
+
 TEST_F(HttpServerPropertiesManagerTest, SupportsQuic) {
   ExpectPrefsUpdate();
   ExpectScheduleUpdatePrefsOnNetworkThread();