[fuchsia] migrate touch-input integration tests to gfx scene manager test ui stack (flutter/engine#41118)

This change migrates `touch-input` integration tests from the
`gfx-root-presenter-test-ui-stack` UI test realm variant to run
parameterized tests of two types: `gfx-scene-manager-test-ui-stack` and
`flatland-scene-manager-test-ui-stack`. Both are exercised for the
generic tap test, and only GFX is exercised for embedded view cases.
This will enable fuchsia.git to remove the
`gfx-root-presenter-test-ui-stack` variant, which will no longer be
supported.

This change also:
- removes or updates all remaining references of root presenter, which
manifested in the form of inline code comments
- adds a TODO to update the child view app for the embedded touch input
test cases

Note that this change does _not_ modify the `embedder` integration
tests, which use a generic `test-ui-stack` variant as defined by the
fuchsia pkg url:
`fuchsia-pkg://fuchsia.com/test-ui-stack#meta/test-ui-stack.cm`. Since
the contents of this package is defined in fuchsia.git, the realm under
test can adapt to changes in fuchsia.git so long as they update the
test-ui-stack build target (which they do in https://fxrev.dev/831359,
the change that relies on the touch changes in this repo described
above.)

Fixes https://fxbug.dev/125304

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide] and the [C++,
Objective-C, Java style guides].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I added new tests to check the change I am making or feature I am
adding, or Hixie said the PR is test-exempt. See [testing the engine]
for instructions on writing and running engine tests.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I signed the [CLA].
- [x] All existing and new tests are passing.

engine/src/flutter/shell/platform/fuchsia/flutter/tests/fakes/scenic/fake_session.h

@@ -59,7 +59,6 @@ namespace flutter_runner::testing {
 //   +Error handling / session disconnection is still WIP.  FakeSession will
 //   likely generate a CHECK in any place where the real scenic would disconnect
 //   the session or send a ScenicError.
-//   +root_presenter-only commands e.g. CreateLayer are not handled.
 //   +Deprecated / obsolete commands are not handled.
 //   +Input is not handled.
 //   +Rendering is not handled.

engine/src/flutter/shell/platform/fuchsia/flutter/tests/integration/touch-input/embedding-flutter-view/lib/embedding-flutter-view.dart

@@ -31,6 +31,7 @@ void main(List<String> args) {
     print('embedding-flutter-view args: $option: ${arguments[option]}');
   }
 
+  // TODO(fxbug.dev/125514): Support Flatland Child View.
   TestApp app = TestApp(
     ChildView.gfx(_launchGfxChildView()),
     showOverlay: arguments['showOverlay'],

engine/src/flutter/shell/platform/fuchsia/flutter/tests/integration/touch-input/meta/touch-input-test.cml

@@ -55,7 +55,8 @@
         "fuchsia.test": {
             "deprecated-allowed-packages": [
                 "embedding-flutter-view",
-                "gfx-root-presenter-test-ui-stack",
+                "gfx-scene-manager-test-ui-stack",
+                "flatland-scene-manager-test-ui-stack",
                 "oot_flutter_aot_runner",
                 "oot_flutter_jit_runner",
                 "oot_flutter_jit_product_runner",

engine/src/flutter/shell/platform/fuchsia/flutter/tests/integration/touch-input/touch-input-test.cc

@@ -51,13 +51,12 @@
 // This test exercises the touch input dispatch path from Input Pipeline to a
 // Scenic client. It is a multi-component test, and carefully avoids sleeping or
 // polling for component coordination.
-// - It runs real Root Presenter, Input Pipeline, and Scenic components.
+// - It runs real Scene Manager and Scenic components.
 // - It uses a fake display controller; the physical device is unused.
 //
 // Components involved
 // - This test program
-// - Input Pipeline
-// - Root Presenter
+// - Scene Manager
 // - Scenic
 // - Child view, a Scenic client
 //
@@ -66,7 +65,7 @@
 //
 // Setup sequence
 // - The test sets up this view hierarchy:
-//   - Top level scene, owned by Root Presenter.
+//   - Top level scene, owned by Scene Manager.
 //   - Child view, owned by the ui client.
 // - The test waits for a Scenic event that verifies the child has UI content in
 // the scene graph.
@@ -128,8 +127,11 @@ using RealmBuilder = component_testing::RealmBuilder;
 // Set this as low as you can that still works across all test platforms.
 constexpr zx::duration kTimeout = zx::min(1);
 
+constexpr auto kGfxTestUIStackUrl =
+    "fuchsia-pkg://fuchsia.com/gfx-scene-manager-test-ui-stack#meta/"
+    "test-ui-stack.cm";
 constexpr auto kTestUIStackUrl =
-    "fuchsia-pkg://fuchsia.com/gfx-root-presenter-test-ui-stack#meta/"
+    "fuchsia-pkg://fuchsia.com/flatland-scene-manager-test-ui-stack#meta/"
     "test-ui-stack.cm";
 
 constexpr auto kMockTouchInputListener = "touch_input_listener";
@@ -424,11 +426,12 @@ class FlutterEmbedTapTest : public FlutterTapTestBase {
 
 // Makes use of gtest's parameterized testing, allowing us
 // to test different combinations of test-ui-stack + runners. Currently, there
-// is just one combination. Documentation:
+// are both GFX and Flatland variants. Documentation:
 // http://go/gunitadvanced#value-parameterized-tests
 INSTANTIATE_TEST_SUITE_P(FlutterTapTestParameterized,
                          FlutterTapTest,
-                         ::testing::Values(kTestUIStackUrl));
+                         ::testing::Values(kGfxTestUIStackUrl,
+                                           kTestUIStackUrl));
 
 TEST_P(FlutterTapTest, FlutterTap) {
   // Launch client view, and wait until it's rendering to proceed with the test.
@@ -454,9 +457,11 @@ TEST_P(FlutterTapTest, FlutterTap) {
   ASSERT_EQ(touch_injection_request_count(), 1);
 }
 
+// TODO(fxbug.dev/125514): Embedded Child View needs to support Flatland.
+// Only test GFX Test UI stack for embedded test cases for now.
 INSTANTIATE_TEST_SUITE_P(FlutterEmbedTapTestParameterized,
                          FlutterEmbedTapTest,
-                         ::testing::Values(kTestUIStackUrl));
+                         ::testing::Values(kGfxTestUIStackUrl));
 
 TEST_P(FlutterEmbedTapTest, FlutterEmbedTap) {
   // Launch view