[camera][draft] Add camera plugin (#29)

Added the first draft version, but there are still a lot of unimplemented features.

packages/camera/elinux/method_channel/method_channel_camera.cc

@@ -0,0 +1,33 @@
+// Copyright 2021 Sony Group Corporation. All rights reserved.
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "method_channel/method_channel_camera.h"
+
+#include <flutter/standard_method_codec.h>
+
+namespace {
+constexpr char kChannelName[] = "flutter.io/cameraPlugin/camera";
+constexpr char kChannelMethodInitialized[] = "initialized";
+};  // namespace
+
+MethodChannelCamera::MethodChannelCamera(flutter::PluginRegistrar* registrar,
+                                         int64_t camera_id) {
+  std::string channel_name = kChannelName + std::to_string(camera_id);
+  channel_ = std::make_unique<flutter::MethodChannel<flutter::EncodableValue>>(
+      registrar->messenger(), channel_name.c_str(),
+      &flutter::StandardMethodCodec::GetInstance());
+}
+
+void MethodChannelCamera::SendInitializedEvent(
+    CameraInitializedEvent& message) {
+  auto value = std::make_unique<flutter::EncodableValue>(message.ToMap());
+  Send(kChannelMethodInitialized, std::move(value));
+}
+
+void MethodChannelCamera::Send(
+    const std::string& method,
+    std::unique_ptr<flutter::EncodableValue>&& arguments) {
+  channel_->InvokeMethod(method, std::move(arguments));
+}