Add a virtual-display (VD) platform view test, and refactor tests a bit. (#161349)

Towards https://github.com/flutter/flutter/issues/161261.

Still need to add a HC (Hybrid Composition) variant, but figured I'd do
this incrementally to make it easier to review.

dev/tools/android_driver_extensions/lib/extension.dart

@@ -49,10 +49,14 @@ final class NativeDriverCommandExtension implements CommandExtension {
     if (result == null) {
       return const _MethodChannelResult(<String, Object?>{});
     }
-    if (result is! Map<String, Object?>) {
-      throw ArgumentError.value(result, 'result', 'Expected a Map<String, Object?>');
+    if (result is! Map<Object?, Object?>) {
+      throw ArgumentError.value(
+        result,
+        'result',
+        'Expected a Map<String, Object?>, got ${result.runtimeType}',
+      );
     }
-    return _MethodChannelResult(result);
+    return _MethodChannelResult(result.cast());
   }
 
   // While these could have been implemented in native code, they are already

dev/tools/android_driver_extensions/lib/src/backend/android/driver.dart

@@ -71,6 +71,12 @@ final class AndroidNativeDriver implements NativeDriver {
     await _driver.sendCommand(NativeCommand.tap(finder));
   }
 
+  @override
+  Future<int> get sdkVersion async {
+    final Map<String, Object?> result = await _driver.sendCommand(NativeCommand.getSdkVersion);
+    return result['version']! as int;
+  }
+
   /// Waits for 2 seconds before completing.
   ///
   /// There is no perfect way, outside of polling, to know when the device is

dev/tools/android_driver_extensions/lib/src/common.dart

@@ -27,6 +27,9 @@ final class NativeCommand extends Command {
   /// Pings the device to ensure it is responsive.
   static const NativeCommand ping = NativeCommand('ping');
 
+  /// Gets the SDK version code.
+  static const NativeCommand getSdkVersion = NativeCommand('sdk_version');
+
   /// The method to call on the plugin.
   final String method;
 

dev/tools/android_driver_extensions/lib/src/driver.dart

@@ -45,6 +45,9 @@ abstract interface class NativeDriver {
   /// ```
   Future<Duration> ping();
 
+  /// Returns the SDK version.
+  Future<int> get sdkVersion;
+
   /// Take a screenshot using a platform-specific mechanism.
   ///
   /// The image is returned as an opaque handle that can be used to retrieve