Convert test to QuitClosure

Use a QuitClosure instead of RunUntilIdle in the CupsPrintersHandlerTest.
Test started failing if CupsPrinterManager creation was delayed.

Bug: 954623
Change-Id: I0ce986ce0995f678197b88c06186737ab56787aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1579325Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653650}

chrome/browser/ui/webui/settings/chromeos/cups_printers_handler_unittest.cc

@@ -42,8 +42,11 @@ void AddedPrinter(int32_t status) {
 }
 
 // Callback used for testing CupsRemovePrinter().
-void RemovedPrinter(bool* expected, bool result) {
-  EXPECT_EQ(*expected, result);
+void RemovedPrinter(base::OnceClosure quit_closure,
+                    bool* expected,
+                    bool result) {
+  *expected = result;
+  std::move(quit_closure).Run();
 }
 
 class FakePrinterConfigurer : public PrinterConfigurer {
@@ -135,11 +138,14 @@ TEST_F(CupsPrintersHandlerTest, RemoveCorrectPrinter) {
 
   // We expect this printer removal to fail since the printer should have
   // already been removed by the previous call to 'removeCupsPrinter'.
-  bool expected = false;
-  client->CupsRemovePrinter("testprinter1",
-                            base::BindRepeating(&RemovedPrinter, &expected),
-                            base::DoNothing());
-  thread_bundle_.RunUntilIdle();
+  base::RunLoop run_loop;
+  bool expected = true;
+  client->CupsRemovePrinter(
+      "testprinter1",
+      base::BindRepeating(&RemovedPrinter, run_loop.QuitClosure(), &expected),
+      base::DoNothing());
+  run_loop.Run();
+  EXPECT_FALSE(expected);
 }
 
 }  // namespace settings.