Re-merge Switch web-render option default to auto. Add documentation

lib/web_ui/dev/README.md

@@ -49,6 +49,8 @@ To run unit tests only:
 felt test --unit-tests-only
 ```
 
+Most of the unit tests are run using the html rendering backends. The unit tests under `test/cancaskit` directory use `canvaskit` backend.
+
 To run integration tests only. For now these tests are only available on Chrome Desktop browsers. These tests will fetch the flutter repository for using `flutter drive` and `flutter pub get` commands. The repository will be synced to the youngest commit older than the engine commit.
 
 ```
@@ -61,6 +63,12 @@ To skip cloning the flutter repository use the following flag. This flag can sav
 felt test --integration-tests-only --use-system-flutter
 ```
 
+We can use different rendering backends for running the integrations tests. If one wants to use html backend use the following command. `web-renderer` flag accepts 3 different options: `html`, `canvaskit`, `auto`.
+
+```
+felt test --integration-tests-only --web-renderer=html
+```
+
 To run tests on Firefox (this will work only on a Linux device):
 
 ```

lib/web_ui/dev/test_runner.dart

@@ -619,6 +619,8 @@ class TestCommand extends Command<bool> with ArgUtils {
       '--enable-experiment=non-nullable',
       '--no-sound-null-safety',
       if (input.forCanvasKit) '-DFLUTTER_WEB_USE_SKIA=true',
+      if (!input.forCanvasKit) '-DFLUTTER_WEB_AUTO_DETECT=false',
+      if (!input.forCanvasKit) '-DFLUTTER_WEB_USE_SKIA=false',
       '-O2',
       '-o',
       targetFileName, // target path.

lib/web_ui/lib/src/engine/canvaskit/initialization.dart

@@ -31,7 +31,7 @@ bool _detectRenderer() {
 /// Using flutter tools option "--web-render=auto" would set the value to true.
 /// Otherwise, it would be false.
 const bool _autoDetect =
-    bool.fromEnvironment('FLUTTER_WEB_AUTO_DETECT', defaultValue: false);
+    bool.fromEnvironment('FLUTTER_WEB_AUTO_DETECT', defaultValue: true);
 
 /// Enable the Skia-based rendering backend.
 ///