[Extensions] Only disable a test on Windows.

I tested 3000 iterations of the ExtensionTabsTest.GetAllWindowsAllTypes
and it was only flaky on Windows:

linux-rel: 0/3000
linux-chromeos-rel: 0/3000
win10_chromium_x64_rel_ng: 6/3000

Bug: 1035620
Change-Id: Ia25c0a0e14c4b2c38d5443a45f23f3e38fcff819
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2142333Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757879}

chrome/browser/extensions/api/tabs/tabs_test.cc

@@ -343,8 +343,13 @@ IN_PROC_BROWSER_TEST_F(ExtensionTabsTest, GetAllWindows) {
   CloseAppWindow(app_window);
 }
 
-// Flaky. https://crbug.com/1035620
-IN_PROC_BROWSER_TEST_F(ExtensionTabsTest, DISABLED_GetAllWindowsAllTypes) {
+// Flaky on Windows. https://crbug.com/1035620
+#if defined(OS_WIN)
+#define MAYBE_GetAllWindowsAllTypes DISABLED_GetAllWindowsAllTypes
+#else
+#define MAYBE_GetAllWindowsAllTypes GetAllWindowsAllTypes
+#endif
+IN_PROC_BROWSER_TEST_F(ExtensionTabsTest, MAYBE_GetAllWindowsAllTypes) {
   const size_t NUM_WINDOWS = 5;
   std::set<int> window_ids;
   std::set<int> result_ids;