WebApp: Do not call SyncInstallDelegate on empty arguments.

Fix WebAppSyncBridge::ApplySyncChangesToRegistrar: Do not call
SyncInstallDelegate methods if app sets are empty.

Add WebAppSyncBridge unit tests for ApplySyncChanges method.

These tests is a promised follow up for this CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1830494

This code is disabled by default behind kDesktopPWAsWithoutExtensions and
kDesktopPWAsUSS base features.

In next CL:
Add WebAppSyncBridge::CommitUpdate unit tests (UpdateSync).

Change-Id: If5b20b3ef8490397a4e024e3237b0456e06667ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1910985
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714825}

chrome/browser/web_applications/test/test_web_app_registry_controller.cc

@@ -57,6 +57,11 @@ void TestWebAppRegistryController::SetInstallWebAppsAfterSyncDelegate(
   install_web_apps_after_sync_delegate_ = delegate;
 }
 
+void TestWebAppRegistryController::SetUninstallWebAppsAfterSyncDelegate(
+    UninstallWebAppsAfterSyncDelegate delegate) {
+  uninstall_web_apps_after_sync_delegate_ = delegate;
+}
+
 void TestWebAppRegistryController::InstallWebAppsAfterSync(
     std::vector<WebApp*> web_apps,
     RepeatingInstallCallback callback) {
@@ -71,8 +76,12 @@ void TestWebAppRegistryController::InstallWebAppsAfterSync(
 void TestWebAppRegistryController::UninstallWebAppsAfterSync(
     std::vector<std::unique_ptr<WebApp>> web_apps,
     RepeatingUninstallCallback callback) {
-  for (const std::unique_ptr<WebApp>& web_app : web_apps)
-    callback.Run(web_app->app_id(), /*uninstalled=*/true);
+  if (uninstall_web_apps_after_sync_delegate_) {
+    uninstall_web_apps_after_sync_delegate_.Run(std::move(web_apps), callback);
+  } else {
+    for (const std::unique_ptr<WebApp>& web_app : web_apps)
+      callback.Run(web_app->app_id(), /*uninstalled=*/true);
+  }
 }
 
 void TestWebAppRegistryController::DestroySubsystems() {

chrome/browser/web_applications/test/test_web_app_registry_controller.h

@@ -44,6 +44,12 @@ class TestWebAppRegistryController : public SyncInstallDelegate {
   void SetInstallWebAppsAfterSyncDelegate(
       InstallWebAppsAfterSyncDelegate delegate);
 
+  using UninstallWebAppsAfterSyncDelegate = base::RepeatingCallback<void(
+      std::vector<std::unique_ptr<WebApp>> web_apps,
+      RepeatingUninstallCallback callback)>;
+  void SetUninstallWebAppsAfterSyncDelegate(
+      UninstallWebAppsAfterSyncDelegate delegate);
+
   // SyncInstallDelegate:
   void InstallWebAppsAfterSync(std::vector<WebApp*> web_apps,
                                RepeatingInstallCallback callback) override;
@@ -60,6 +66,7 @@ class TestWebAppRegistryController : public SyncInstallDelegate {
 
  private:
   InstallWebAppsAfterSyncDelegate install_web_apps_after_sync_delegate_;
+  UninstallWebAppsAfterSyncDelegate uninstall_web_apps_after_sync_delegate_;
 
   std::unique_ptr<TestWebAppDatabaseFactory> database_factory_;
   std::unique_ptr<WebAppRegistrarMutable> mutable_registrar_;

chrome/browser/web_applications/web_app_sync_bridge.cc

@@ -395,14 +395,18 @@ void WebAppSyncBridge::ApplySyncChangesToRegistrar(
 
   // Do a full follow up install for all remote entities that don’t exist
   // locally.
-  install_delegate_->InstallWebAppsAfterSync(std::move(apps_to_install),
-                                             base::DoNothing());
+  if (!apps_to_install.empty()) {
+    install_delegate_->InstallWebAppsAfterSync(std::move(apps_to_install),
+                                               base::DoNothing());
+  }
 
   // Do a full follow up uninstall for all deleted remote entities that exist
   // locally and not needed by other sources. We need to clean up disk data
   // (icons).
-  install_delegate_->UninstallWebAppsAfterSync(std::move(apps_unregistered),
-                                               base::DoNothing());
+  if (!apps_unregistered.empty()) {
+    install_delegate_->UninstallWebAppsAfterSync(std::move(apps_unregistered),
+                                                 base::DoNothing());
+  }
 }
 
 std::unique_ptr<syncer::MetadataChangeList>