[Linux] Fix channel buffers control commands error handling (#45056)

## Description

This PR fixes a mistake I made on #44636 where the error handling code wrongly relied on `fl_method_channel_invoke_method_finish` instead of  `fl_binary_messenger_send_on_channel_finish`.
The error handling code was not called when running the tests added in #44636 so this mistake did not pop up.

@robert-ancell I added a test that simulates an error response and I had to rely on `g_idle_add` to make it works. Is this approach ok?

## Related Issue

Linux implementation for flutter/flutter#132386

## Tests

Adds one test.

Author: bleroux

shell/platform/linux/fl_binary_messenger.cc

@@ -324,12 +324,14 @@ static GBytes* send_on_channel_finish(FlBinaryMessenger* messenger,
 static gboolean finish_method(GObject* object,
                               GAsyncResult* result,
                               GError** error) {
-  g_autoptr(FlMethodResponse) response = fl_method_channel_invoke_method_finish(
-      FL_METHOD_CHANNEL(object), result, error);
+  g_autoptr(GBytes) response = fl_binary_messenger_send_on_channel_finish(
+      FL_BINARY_MESSENGER(object), result, error);
   if (response == nullptr) {
     return FALSE;
   }
-  return fl_method_response_get_result(response, error) != nullptr;
+  g_autoptr(FlStandardMethodCodec) codec = fl_standard_method_codec_new();
+  return fl_method_codec_decode_response(FL_METHOD_CODEC(codec), response,
+                                         error) != nullptr;
 }
 
 // Called when a response is received for the resize channel message.

shell/platform/linux/fl_binary_messenger_test.cc

@@ -501,6 +501,56 @@ TEST(FlBinaryMessengerTest, AllowOverflowChannel) {
   EXPECT_TRUE(called);
 }
 
+static gboolean quit_main_loop_cb(gpointer user_data) {
+  g_main_loop_quit(static_cast<GMainLoop*>(user_data));
+  return FALSE;
+}
+
+// Checks if error returned when invoking a command on the control channel
+// are handled.
+TEST(FlBinaryMessengerTest, ControlChannelErrorResponse) {
+  g_autoptr(GMainLoop) loop = g_main_loop_new(nullptr, 0);
+  g_autoptr(FlEngine) engine = make_mock_engine();
+  FlBinaryMessenger* messenger = fl_binary_messenger_new(engine);
+
+  g_autoptr(GError) error = nullptr;
+  EXPECT_TRUE(fl_engine_start(engine, &error));
+  EXPECT_EQ(error, nullptr);
+
+  FlutterEngineProcTable* embedder_api = fl_engine_get_embedder_api(engine);
+
+  bool called = false;
+
+  FlutterEngineSendPlatformMessageFnPtr old_handler =
+      embedder_api->SendPlatformMessage;
+  embedder_api->SendPlatformMessage = MOCK_ENGINE_PROC(
+      SendPlatformMessage,
+      ([&called, old_handler, loop](auto engine,
+                                    const FlutterPlatformMessage* message) {
+        // Expect to receive a message on the "control" channel.
+        if (strcmp(message->channel, "dev.flutter/channel-buffers") != 0) {
+          return old_handler(engine, message);
+        }
+
+        called = true;
+
+        // Register a callback to quit the main loop when binary messenger work
+        // ends.
+        g_idle_add(quit_main_loop_cb, loop);
+
+        // Simulates an internal error.
+        return kInvalidArguments;
+      }));
+
+  fl_binary_messenger_set_allow_channel_overflow(messenger, "flutter/test",
+                                                 true);
+
+  EXPECT_TRUE(called);
+
+  // Blocks here until quit_main_loop_cb is called.
+  g_main_loop_run(loop);
+}
+
 // NOLINTEND(clang-analyzer-core.StackAddressEscape)
 
 struct RespondsOnBackgroundThreadInfo {