[Telemetry SWX] Use FlushForTesting instead of RunUntilIdle

Use new method ServiceConnection::FlushForTesting instead of
RunUntilIdle.

Change-Id: Idfa4a5fdd3eb8ab43be0d5ed527e334a6401c821
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2398624Reviewed-by: Mahmoud Gawad <mgawad@google.com>
Commit-Queue: Oleh Lamzin <lamzin@google.com>
Cr-Commit-Position: refs/heads/master@{#805657}

chromeos/components/telemetry_extension_ui/BUILD.gn

@@ -54,6 +54,7 @@ source_set("unit_tests") {
     "//chrome/browser/chromeos/wilco_dtc_supportd:mojo_utils",
     "//chromeos/components/telemetry_extension_ui/mojom",
     "//chromeos/dbus/cros_healthd",
+    "//chromeos/services/cros_healthd/public/cpp",
     "//chromeos/services/cros_healthd/public/mojom",
     "//testing/gmock",
     "//testing/gtest",

chromeos/components/telemetry_extension_ui/probe_service_unittest.cc

@@ -16,6 +16,7 @@
 #include "base/test/task_environment.h"
 #include "chromeos/dbus/cros_healthd/cros_healthd_client.h"
 #include "chromeos/dbus/cros_healthd/fake_cros_healthd_client.h"
+#include "chromeos/services/cros_healthd/public/cpp/service_connection.h"
 #include "mojo/public/cpp/bindings/remote.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -28,9 +29,8 @@ class ProbeServiceTest : public testing::Test {
   void TearDown() override {
     CrosHealthdClient::Shutdown();
 
-    // Wait for cros_healthd::ServiceConnection to observe the destruction of
-    // the client.
-    base::RunLoop().RunUntilIdle();
+    // Wait for ServiceConnection to observe the destruction of the client.
+    cros_healthd::ServiceConnection::GetInstance()->FlushForTesting();
   }
 
   health::mojom::ProbeServiceProxy* probe_service() const {