Do not allow GuestViewManager to (re)use an instance ID that was already removed.

chrome/chrome_tests_unit.gypi

Index: chrome/chrome_tests_unit.gypi
diff --git a/chrome/chrome_tests_unit.gypi b/chrome/chrome_tests_unit.gypi
index a97c1b1f6ee537d3d4132f7dd5bca9f1844d32d7..e472ad8981d5480049fee9c00a8903b39aacdcfb 100644
--- a/chrome/chrome_tests_unit.gypi
+++ b/chrome/chrome_tests_unit.gypi
@@ -599,7 +599,7 @@
         'browser/autocomplete/search_provider_unittest.cc',
         'browser/autocomplete/shortcuts_backend_unittest.cc',
         'browser/autocomplete/shortcuts_provider_unittest.cc',
-	'browser/autocomplete/zero_suggest_provider_unittest.cc',
+        'browser/autocomplete/zero_suggest_provider_unittest.cc',
         'browser/autofill/autofill_cc_infobar_delegate_unittest.cc',
         'browser/background/background_application_list_model_unittest.cc',
         'browser/background/background_contents_service_unittest.cc',
@@ -985,6 +985,7 @@
         'browser/google/google_update_settings_unittest.cc',
         'browser/google/google_url_tracker_unittest.cc',
         'browser/google/google_util_unittest.cc',
+        'browser/guest_view/guest_view_manager_unittest.cc',
         'browser/history/android/android_cache_database_unittest.cc',
         'browser/history/android/android_history_provider_service_unittest.cc',
         'browser/history/android/android_history_types_unittest.cc',