Fix SystemWebAppManagerUpgradeBrowserTest warning on non Chrome OS

This CL fixes the following warning in browser_tests on non Chrome OS:
UninstantiatedParamaterizedTestSuite<SystemWebAppManagerUpgradeBrowserTest>

Bug: 1045846
Change-Id: I26aff6a78626ad899237e62ef0eb1081a0d07bf7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2331253
Commit-Queue: Alan Cutter <alancutter@chromium.org>
Commit-Queue: Jiewei Qian  <qjw@chromium.org>
Auto-Submit: Alan Cutter <alancutter@chromium.org>
Reviewed-by: Jiewei Qian  <qjw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793503}

chrome/browser/web_applications/system_web_app_manager_browsertest.cc

@@ -1026,6 +1026,9 @@ IN_PROC_BROWSER_TEST_P(SystemWebAppManagerUninstallBrowserTest, Uninstall) {
   EXPECT_TRUE(GetManager().GetAppIds().empty());
 }
 
+// We only have concrete System Web Apps on Chrome OS.
+#if defined(OS_CHROMEOS)
+
 // Test that all registered System Apps can be re-installed.
 class SystemWebAppManagerUpgradeBrowserTest
     : public SystemWebAppManagerBrowserTest {
@@ -1061,6 +1064,8 @@ IN_PROC_BROWSER_TEST_P(SystemWebAppManagerUpgradeBrowserTest, Upgrade) {
   }
 }
 
+#endif  // defined(OS_CHROMEOS)
+
 // Tests that SWA-specific data is correctly migrated to Web Apps without
 // Extensions.
 class SystemWebAppManagerMigrationTest
@@ -1532,7 +1537,6 @@ INSTANTIATE_TEST_SUITE_P(All,
                                            ProviderType::kWebApps),
                          ProviderTypeParamToString);
 
-// We only have concrete System Web Apps on Chrome OS.
 #if defined(OS_CHROMEOS)
 INSTANTIATE_TEST_SUITE_P(All,
                          SystemWebAppManagerUpgradeBrowserTest,