Fix flakiness of ExtensionBrowserTest

the extension to be loaded, so remove RunLoop::RunUntilIdle
which causes the flaky tests.

ChromeTestExtensionLoader: :LoadExtension is already waiting for
Change-Id: I7c7727617e93b2152e84ec32532ab084b889c745
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1743242Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#685199}

chrome/browser/extensions/chrome_test_extension_loader.cc

@@ -133,7 +133,6 @@ scoped_refptr<const Extension> ChromeTestExtensionLoader::LoadExtension(
   if (!CheckInstallWarnings(*extension))
     return nullptr;
 
-  base::RunLoop().RunUntilIdle();
   if (!WaitForExtensionReady(*extension)) {
     ADD_FAILURE() << "Failed to wait for extension ready";
     return nullptr;

chrome/browser/ui/views/toolbar/toolbar_view_interactive_uitest.cc

@@ -157,9 +157,6 @@ IN_PROC_BROWSER_TEST_F(ToolbarViewInteractiveUITest,
   ASSERT_TRUE(LoadExtension(test_data_dir_.AppendASCII("api_test")
                                           .AppendASCII("browser_action")
                                           .AppendASCII("basics")));
-  // Ensure the extension is fully loaded, and that the next steps will happen
-  // with a clean slate.
-  base::RunLoop().RunUntilIdle();
 
   // Set up observers that will drive the test along.
   AppMenuButton* const app_menu_button = GetAppMenuButton();