arc: Partially migrate mojo types

chrome/browser/chromeos/arc/downloads_watcher/arc_downloads_watcher_service.cc

Index: chrome/browser/chromeos/arc/downloads_watcher/arc_downloads_watcher_service.cc
diff --git a/chrome/browser/chromeos/arc/downloads_watcher/arc_downloads_watcher_service.cc b/chrome/browser/chromeos/arc/downloads_watcher/arc_downloads_watcher_service.cc
index 21d5f69720639e416502ab9fb20ec7fb770507e2..8663dd43993c59cf61dec719b64bea0a09166391 100644
--- a/chrome/browser/chromeos/arc/downloads_watcher/arc_downloads_watcher_service.cc
+++ b/chrome/browser/chromeos/arc/downloads_watcher/arc_downloads_watcher_service.cc
@@ -10,9 +10,7 @@
 #include <iterator>
 #include <map>
 #include <memory>
-#include <string>
 #include <utility>
-#include <vector>
 
 #include "base/callback.h"
 #include "base/files/file_enumerator.h"
@@ -186,7 +184,7 @@ bool HasAndroidSupportedMediaExtension(const base::FilePath& path) {
 // Downloads directory.
 class ArcDownloadsWatcherService::DownloadsWatcher {
  public:
-  using Callback = base::Callback<void(mojo::Array<mojo::String> paths)>;
+  using Callback = base::Callback<void(std::vector<std::string> paths)>;
 
   explicit DownloadsWatcher(const Callback& callback);
   ~DownloadsWatcher();
@@ -296,7 +294,7 @@ void ArcDownloadsWatcherService::DownloadsWatcher::OnBuildTimestampMap(
 
   last_timestamp_map_ = std::move(current_timestamp_map);
 
-  mojo::Array<mojo::String> mojo_paths(changed_paths.size());
+  std::vector<std::string> mojo_paths(changed_paths.size());
   for (size_t i = 0; i < changed_paths.size(); ++i) {
     mojo_paths[i] = changed_paths[i].value();
   }
@@ -359,7 +357,7 @@ void ArcDownloadsWatcherService::StopWatchingDownloads() {
 }
 
 void ArcDownloadsWatcherService::OnDownloadsChanged(
-    mojo::Array<mojo::String> paths) {
+    std::vector<std::string> paths) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
   auto* instance = arc_bridge_service()->file_system()->GetInstanceForMethod(