Re-enable SingleClientThemesSyncTest.NativeTheme on ChromeOS

According to the linked bug, the reason for disabling the test has been
long resolved.

Bug: 84575
Change-Id: I21847fb8199ddedae72db3d58facc7f801db1453
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1796423
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Auto-Submit: Marc Treib <treib@chromium.org>
Reviewed-by: Jan Krcal <jkrcal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695536}

chrome/browser/sync/test/integration/single_client_themes_sync_test.cc

@@ -54,12 +54,7 @@ IN_PROC_BROWSER_TEST_F(SingleClientThemesSyncTest, CustomTheme) {
   EXPECT_EQ(GetCustomTheme(0), GetThemeID(verifier()));
 }
 
-// TODO(sync): Fails on Chrome OS. See http://crbug.com/84575.
-#if defined(OS_CHROMEOS)
-IN_PROC_BROWSER_TEST_F(SingleClientThemesSyncTest, DISABLED_NativeTheme) {
-#else
 IN_PROC_BROWSER_TEST_F(SingleClientThemesSyncTest, NativeTheme) {
-#endif  // OS_CHROMEOS
   ASSERT_TRUE(SetupSync()) << "SetupSync() failed.";
 
   SetCustomTheme(GetProfile(0));