Implement mediaGalleriesPrivate api to notify extensions about gallery changed events.

chrome/browser/media_gallery/media_galleries_test_util.cc

Index: chrome/browser/media_gallery/media_galleries_test_util.cc
diff --git a/chrome/browser/media_gallery/media_galleries_test_util.cc b/chrome/browser/media_gallery/media_galleries_test_util.cc
index 8c7635ce2cd6c9af50cb890a3b49f60537f6c5dc..6bf1626f7eaae012e5b1ef6f47ea4c3fd6d01a5c 100644
--- a/chrome/browser/media_gallery/media_galleries_test_util.cc
+++ b/chrome/browser/media_gallery/media_galleries_test_util.cc
@@ -69,6 +69,23 @@ EnsureMediaDirectoriesExists::EnsureMediaDirectoriesExists()
   Init();
 }
 
+bool EnsureMediaDirectoriesExists::AddNewFileInGallery(
+    int gallery_directory_key) {
+  if ((gallery_directory_key != chrome::DIR_USER_MUSIC) &&
+      (gallery_directory_key != chrome::DIR_USER_PICTURES) &&
+      (gallery_directory_key != chrome::DIR_USER_VIDEOS))
+    return false;
+
+  FilePath gallery_dir;
+  PathService::Get(gallery_directory_key, &gallery_dir);
+  FilePath gallery_file =
+    gallery_dir.Append(FILE_PATH_LITERAL("test1.txt"));
+  std::string content("new content");
+  int write_size = file_util::WriteFile(gallery_file, content.c_str(),
+                                        content.length());
+  return (write_size == static_cast<int>(content.length()));
+}
+
 void EnsureMediaDirectoriesExists::Init() {
 #if defined(OS_CHROMEOS) || defined(OS_ANDROID)
   return;