AllSites: Fix flaky test.

Applies the fix suggested by dbertoni@ on the bug:

Adds a TearDown method which calls
StoragePartition::WaitForDeletionTasksForTesting() to wait for all
deletion tasks to finish and make sure QuotaDatabase does not
run into out of disk space errors.

Bug: 930481
Change-Id: I1d2203d0b6d817ef84ccbda206ab216e54f4fd80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2307644Reviewed-by: Martin Šrámek <msramek@chromium.org>
Commit-Queue: Jarryd Goodman <jarrydg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791486}

chrome/browser/ui/webui/settings/site_settings_handler_unittest.cc

@@ -54,6 +54,7 @@
 #include "components/sync_preferences/testing_pref_service_syncable.h"
 #include "components/ukm/test_ukm_recorder.h"
 #include "content/public/browser/navigation_controller.h"
+#include "content/public/browser/storage_partition.h"
 #include "content/public/browser/web_ui_data_source.h"
 #include "content/public/test/browser_task_environment.h"
 #include "content/public/test/test_web_ui.h"
@@ -209,6 +210,15 @@ class SiteSettingsHandlerTest : public testing::Test {
     web_ui()->ClearTrackedCalls();
   }
 
+  void TearDown() override {
+    if (profile_) {
+      auto* partition =
+          content::BrowserContext::GetDefaultStoragePartition(profile_.get());
+      if (partition)
+        partition->WaitForDeletionTasksForTesting();
+    }
+  }
+
   TestingProfile* profile() { return profile_.get(); }
   TestingProfile* incognito_profile() { return incognito_profile_; }
   web_app::TestAppRegistrar& app_registrar() { return app_registrar_; }
@@ -548,12 +558,7 @@ TEST_F(SiteSettingsHandlerTest, GetAndSetDefault) {
 }
 
 // Flaky on CrOS and Linux. https://crbug.com/930481
-#if defined(OS_CHROMEOS) || defined(OS_LINUX)
-#define MAYBE_GetAllSites DISABLED_GetAllSites
-#else
-#define MAYBE_GetAllSites GetAllSites
-#endif
-TEST_F(SiteSettingsHandlerTest, MAYBE_GetAllSites) {
+TEST_F(SiteSettingsHandlerTest, GetAllSites) {
   base::ListValue get_all_sites_args;
   get_all_sites_args.AppendString(kCallbackId);
   base::Value category_list(base::Value::Type::LIST);