[Code health] Convert base::Bind in gallery_watch_manager_unittest.cc

This CL converts three base::Bind to base::BindOnce in this file.
The function that takes the callback is already expecting a
OnceCallback, so converting to base::BindOnce seems to be the right
choice.

Bug: 1152278
Change-Id: I0ed76be834d516ccdcb20200b30f172fa41f385a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2592012Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837150}

chrome/browser/media_galleries/gallery_watch_manager_unittest.cc

@@ -159,10 +159,8 @@ class GalleryWatchManagerTest : public GalleryWatchManagerObserver,
 
   void AddAndConfirmWatch(MediaGalleryPrefId gallery_id) {
     base::RunLoop loop;
-    manager()->AddWatch(profile(),
-                        extension(),
-                        gallery_id,
-                        base::Bind(&ConfirmWatch, base::Unretained(&loop)));
+    manager()->AddWatch(profile(), extension(), gallery_id,
+                        base::BindOnce(&ConfirmWatch, base::Unretained(&loop)));
     loop.Run();
   }
 
@@ -230,17 +228,12 @@ TEST_F(GalleryWatchManagerTest, MAYBE_Basic) {
 
   base::RunLoop loop;
   if (GalleryWatchesSupported()) {
-    manager()->AddWatch(profile(),
-                        extension(),
-                        id,
-                        base::Bind(&ConfirmWatch, base::Unretained(&loop)));
+    manager()->AddWatch(profile(), extension(), id,
+                        base::BindOnce(&ConfirmWatch, base::Unretained(&loop)));
   } else {
     manager()->AddWatch(
-        profile(),
-        extension(),
-        id,
-        base::Bind(&ExpectWatchError,
-                   base::Unretained(&loop),
+        profile(), extension(), id,
+        base::BindOnce(&ExpectWatchError, base::Unretained(&loop),
                        GalleryWatchManager::kCouldNotWatchGalleryError));
   }
   loop.Run();