Small fix to the extension test (#1811)

Author: elliette

dwds/test/puppeteer/extension_test.dart

@@ -133,15 +133,14 @@ void main() async {
           // Verify the extension opened the Dart docs in the same window:
           var devToolsTabTarget = await browser.waitForTarget(
               (target) => target.url.contains(devToolsUrlFragment));
-          final devToolsPage = await devToolsTabTarget.page;
+          var devToolsTab = await devToolsTabTarget.page;
           var devToolsWindowId = await _getWindowId(
-            devToolsPage.url!,
+            devToolsTab.url!,
             worker: worker,
           );
           var appWindowId = await _getWindowId(appUrl, worker: worker);
           expect(devToolsWindowId == appWindowId, isTrue);
           // Close the DevTools tab:
-          var devToolsTab = await devToolsTabTarget.page;
           await devToolsTab.close();
           // Navigate to the extension settings page:
           final extensionOrigin = getExtensionOrigin(browser);
@@ -164,8 +163,10 @@ void main() async {
           // Verify the extension opened DevTools in a different window:
           devToolsTabTarget = await browser.waitForTarget(
               (target) => target.url.contains(devToolsUrlFragment));
+          devToolsTab = await devToolsTabTarget.page;
+          await devToolsTab.bringToFront();
           devToolsWindowId = await _getWindowId(
-            devToolsPage.url!,
+            devToolsTab.url!,
             worker: worker,
           );
           appWindowId = await _getWindowId(appUrl, worker: worker);
@@ -197,6 +198,7 @@ void main() async {
           await appTab.bringToFront();
           // Verify that the Dart DevTools tab closes:
           await devToolsTabTarget.onClose;
+          await appTab.close();
         });
 
         test('Closing the Dart app while debugging closes DevTools', () async {