refactor: move impl classes into unnamed namespaces (#42390)

* refactor: move ReplyChannel into an anonymous namespace

* refactor: move ChunkedDataPipeReadableStream into an anonymous namespace

* refactor: move linux helpers into an anonymous namespace

* refactor: move linux helpers into an anonymous namespace

shell/browser/api/electron_api_web_contents.cc

@@ -1893,6 +1893,8 @@ void WebContents::OnFirstNonEmptyLayout(
   }
 }
 
+namespace {
+
 // This object wraps the InvokeCallback so that if it gets GC'd by V8, we can
 // still call the callback and send an error. Not doing so causes a Mojo DCHECK,
 // since Mojo requires callbacks to be called before they are destroyed.
@@ -1949,6 +1951,8 @@ class ReplyChannel : public gin::Wrappable<ReplyChannel> {
 
 gin::WrapperInfo ReplyChannel::kWrapperInfo = {gin::kEmbedderNativeGin};
 
+}  // namespace
+
 gin::Handle<gin_helper::internal::Event> WebContents::MakeEventWithSender(
     v8::Isolate* isolate,
     content::RenderFrameHost* frame,