[webview_flutter_wkebview] Verify JavaScriptChannels have a unique name (#5904)

Fixes flutter/flutter#141242

According to [WKUserContentController.addScriptMessageHandler](https://developer.apple.com/documentation/webkit/wkusercontentcontroller/1537172-addscriptmessagehandler?language=objc), a handler must have a unique name. In flutter/flutter#141242, this led to a crash. This PR prevents the app crash and throws an error from Dart when the method is called.

Author: bparrishMines

CHANGELOG.md

@@ -1,5 +1,7 @@
-## NEXT
+## 3.10.3
 
+* Adds a check that throws an `ArgumentError` when `WebKitWebViewController.addJavaScriptChannel`
+  receives a `JavaScriptChannelParams` with a name that is not unique.
 * Updates minimum iOS version to 12.0 and minimum Flutter version to 3.16.6.
 
 ## 3.10.2

lib/src/webkit_webview_controller.dart

@@ -326,6 +326,13 @@ class WebKitWebViewController extends PlatformWebViewController {
   Future<void> addJavaScriptChannel(
     JavaScriptChannelParams javaScriptChannelParams,
   ) {
+    final String channelName = javaScriptChannelParams.name;
+    if (_javaScriptChannelParams.containsKey(channelName)) {
+      throw ArgumentError(
+        'A JavaScriptChannel with name `$channelName` already exists.',
+      );
+    }
+
     final WebKitJavaScriptChannelParams webKitParams =
         javaScriptChannelParams is WebKitJavaScriptChannelParams
             ? javaScriptChannelParams

pubspec.yaml

@@ -2,7 +2,7 @@ name: webview_flutter_wkwebview
 description: A Flutter plugin that provides a WebView widget based on Apple's WKWebView control.
 repository: https://github.com/flutter/packages/tree/main/packages/webview_flutter/webview_flutter_wkwebview
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+webview%22
-version: 3.10.2
+version: 3.10.3
 
 environment:
   sdk: ^3.2.3

test/webkit_webview_controller_test.dart

@@ -756,6 +756,45 @@ void main() {
       );
     });
 
+    test('addJavaScriptChannel requires channel with a unique name', () async {
+      final WebKitProxy webKitProxy = WebKitProxy(
+        createScriptMessageHandler: ({
+          required void Function(
+            WKUserContentController userContentController,
+            WKScriptMessage message,
+          ) didReceiveScriptMessage,
+        }) {
+          return WKScriptMessageHandler.detached(
+            didReceiveScriptMessage: didReceiveScriptMessage,
+          );
+        },
+      );
+      final MockWKUserContentController mockUserContentController =
+          MockWKUserContentController();
+      final WebKitWebViewController controller = createControllerWithMocks(
+        mockUserContentController: mockUserContentController,
+      );
+
+      const String nonUniqueName = 'name';
+      final WebKitJavaScriptChannelParams javaScriptChannelParams =
+          WebKitJavaScriptChannelParams(
+        name: nonUniqueName,
+        onMessageReceived: (JavaScriptMessage message) {},
+        webKitProxy: webKitProxy,
+      );
+      await controller.addJavaScriptChannel(javaScriptChannelParams);
+
+      expect(
+        () => controller.addJavaScriptChannel(
+          JavaScriptChannelParams(
+            name: nonUniqueName,
+            onMessageReceived: (_) {},
+          ),
+        ),
+        throwsArgumentError,
+      );
+    });
+
     test('removeJavaScriptChannel', () async {
       final WebKitProxy webKitProxy = WebKitProxy(
         createScriptMessageHandler: ({