Make ProfileResetterTest.ResetExtensionsByDisabling more reliable

Wait for theme update by listening for notification instead of
RunUntilIdle. This fix is prospective: I couldn't get it to flake
locally with or without the change.

Bug: 995851
Change-Id: I5a3a4dda389178f6e3dd114ee14da9ea593254d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1762353Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688707}

chrome/browser/profile_resetter/profile_resetter_unittest.cc

@@ -20,6 +20,7 @@
 #include "base/test/bind_test_util.h"
 #include "base/test/scoped_path_override.h"
 #include "build/build_config.h"
+#include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/content_settings/host_content_settings_map_factory.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/extension_service_test_base.h"
@@ -45,6 +46,7 @@
 #include "components/search_engines/template_url_service.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/test/test_browser_thread.h"
+#include "content/public/test/test_utils.h"
 #include "extensions/browser/extension_registry.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/manifest_constants.h"
@@ -508,28 +510,23 @@ TEST_F(ProfileResetterTest, ResetContentSettings) {
   }
 }
 
-#if defined(OS_CHROMEOS)
-// Flaky on ChromeOS: https://crbug.com/995851
-#define MAYBE_ResetExtensionsByDisabling DISABLED_ResetExtensionsByDisabling
-#else
-#define MAYBE_ResetExtensionsByDisabling ResetExtensionsByDisabling
-#endif
-
-TEST_F(ProfileResetterTest, MAYBE_ResetExtensionsByDisabling) {
+TEST_F(ProfileResetterTest, ResetExtensionsByDisabling) {
   service_->Init();
 
   base::ScopedTempDir temp_dir;
   ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
 
+  ThemeService* theme_service = ThemeServiceFactory::GetForProfile(profile());
+  content::WindowedNotificationObserver theme_change_observer(
+      chrome::NOTIFICATION_BROWSER_THEME_CHANGED,
+      content::Source<ThemeService>(theme_service));
+
   scoped_refptr<Extension> theme = CreateExtension(
       base::ASCIIToUTF16("example1"), temp_dir.GetPath(), Manifest::UNPACKED,
       extensions::Manifest::TYPE_THEME, false);
   service_->FinishInstallationForTest(theme.get());
-  // Let ThemeService finish creating the theme pack.
-  base::RunLoop().RunUntilIdle();
+  theme_change_observer.Wait();
 
-  ThemeService* theme_service =
-      ThemeServiceFactory::GetForProfile(profile());
   EXPECT_FALSE(theme_service->UsingDefaultTheme());
 
   scoped_refptr<Extension> ext2 = CreateExtension(