[Extensions] Disable/enable ExtensionServiceTest.InstallTheme.

This test is no longer flaky on asan or tsan bots, but is very flaky
on Mac and Windows, so this CL re-enables the test on the asan/tsan bots
and disables it on Mac and Windows.

Bug: 377702, 1148894
Change-Id: Ia0065e4636bf813d98bca6cda1ead3edc7ae4684
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2535035Reviewed-by: Kelvin Jiang <kelvinjiang@chromium.org>
Commit-Queue: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827478}

chrome/browser/extensions/extension_service_unittest.cc

@@ -2286,13 +2286,12 @@ TEST_F(ExtensionServiceTest, TestInstallThemeWithExtensionsDisabled) {
   ValidateIntegerPref(theme_crx, "location", Manifest::INTERNAL);
 }
 
-#if defined(THREAD_SANITIZER)
-// Flaky under Tsan. http://crbug.com/377702
+#if defined(OS_MAC) || defined(OS_WIN)
+// Flaky on these platforms. http://crbug.com/1148894
 #define MAYBE_InstallTheme DISABLED_InstallTheme
 #else
 #define MAYBE_InstallTheme InstallTheme
 #endif
-
 TEST_F(ExtensionServiceTest, MAYBE_InstallTheme) {
   InitializeEmptyExtensionService();
   service()->Init();