Add testRunner.runIdleTasks() to force idle tasks to run.

components/test_runner/test_runner.h

Index: components/test_runner/test_runner.h
diff --git a/components/test_runner/test_runner.h b/components/test_runner/test_runner.h
index 46f6507fe95e3b944b95556a2620118f9ee1e5c1..bce16942d0e2be4aac64990df56b175c634a5c88 100644
--- a/components/test_runner/test_runner.h
+++ b/components/test_runner/test_runner.h
@@ -588,6 +588,11 @@ class TestRunner : public WebTestRunner {
   void ResolveBeforeInstallPromptPromise(int request_id,
                                          const std::string& platform);
 
+  // Immediately run all pending idle tasks, including all pending
+  // requestIdleCallback calls.  Invoke the callback when all
+  // idle tasks are complete.
+  void RunIdleTasks(v8::Local<v8::Function> callback);
+
   // Calls setlocale(LC_ALL, ...) for a specified locale.
   // Resets between tests.
   void SetPOSIXLocale(const std::string& locale);