Change pass by value to pass by ref to const.

This is a follow up for
https://chromium-review.googlesource.com/c/chromium/src/+/2495332

The idea is that passing input parameters by const references, when
possible is still the C++ style.

I don't recall what the specific issue was when the code did not
build in the original CL. At any rate, this change does not
affect the lifetime of any of the parameters, since the binding
of the references in callbacks is always by value, unless the
caller specifies std::ref of std::cref.

Bug: 1147094
Change-Id: I47c9aef89ddbeea386e6efb9f8ae42d3385c3601
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2547430Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829236}

chrome/updater/control_service_impl.cc

@@ -107,7 +107,8 @@ void ControlServiceImpl::MaybeCheckForUpdates() {
           base::BindOnce(std::move(callback_)), config_));
 }
 
-void ControlServiceImpl::UnregisterMissingApps(std::vector<AppInfo> apps) {
+void ControlServiceImpl::UnregisterMissingApps(
+    const std::vector<AppInfo>& apps) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
   base::ThreadPool::PostTaskAndReplyWithResult(
@@ -123,7 +124,7 @@ void ControlServiceImpl::UnregisterMissingAppsDone() {
 }
 
 std::vector<ControlServiceImpl::PingInfo> ControlServiceImpl::GetAppIDsToRemove(
-    std::vector<AppInfo> apps) {
+    const std::vector<AppInfo>& apps) {
   std::vector<PingInfo> app_ids_to_remove;
   for (const auto& app : apps) {
     // Skip if app_id is equal to updater app id.
@@ -143,7 +144,7 @@ std::vector<ControlServiceImpl::PingInfo> ControlServiceImpl::GetAppIDsToRemove(
 }
 
 void ControlServiceImpl::RemoveAppIDsAndSendUninstallPings(
-    std::vector<PingInfo> app_ids_to_remove) {
+    const std::vector<PingInfo>& app_ids_to_remove) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
   if (app_ids_to_remove.empty()) {
@@ -151,10 +152,10 @@ void ControlServiceImpl::RemoveAppIDsAndSendUninstallPings(
     return;
   }
 
-  for (const auto& app_id_to_remove : app_ids_to_remove) {
-    const auto app_id = app_id_to_remove.app_id_;
+  for (const PingInfo& app_id_to_remove : app_ids_to_remove) {
+    const std::string& app_id = app_id_to_remove.app_id_;
     const int ping_reason = app_id_to_remove.ping_reason_;
-    const base::Version app_version = app_id_to_remove.app_version_;
+    const base::Version& app_version = app_id_to_remove.app_version_;
 
     if (persisted_data_->RemoveApp(app_id)) {
       VLOG(1) << "Uninstall ping for app id: " << app_id

chrome/updater/control_service_impl.h

@@ -75,7 +75,7 @@ class ControlServiceImpl : public ControlService {
 
   // Provides a way to remove apps from the persisted data if the app is no
   // longer installed on the machine.
-  void UnregisterMissingApps(std::vector<AppInfo> apps);
+  void UnregisterMissingApps(const std::vector<AppInfo>& apps);
 
   // After an uninstall ping has been processed, reduces the number of pings
   // that we need to wait on before checking for updates.
@@ -87,12 +87,12 @@ class ControlServiceImpl : public ControlService {
 
   // Returns a list of apps that need to be unregistered.
   std::vector<ControlServiceImpl::PingInfo> GetAppIDsToRemove(
-      std::vector<AppInfo> apps);
+      const std::vector<AppInfo>& apps);
 
   // Unregisters the apps in |app_ids_to_remove| and starts an update check
   // if necessary.
   void RemoveAppIDsAndSendUninstallPings(
-      std::vector<PingInfo> app_ids_to_remove);
+      const std::vector<PingInfo>& app_ids_to_remove);
 
   scoped_refptr<updater::Configurator> config_;
   scoped_refptr<updater::PersistedData> persisted_data_;