win: use UPDATEITEM, not ASSOCCHANGED when updating shortcut

SHCNE_ASSOCCHANGED causes the whole desktop to flash. I've found
that UPDATEITEM is sufficient in other scenarios (crrev.com/c/3442476)
and works better on Win 11. Add SHCNF_FLUSH since some shortcut changes
require it, and this function should be called rarely (and even with
FLUSH should be a lot faster than SHCNE_ASSOCCHANGED)

Tested manually by locally modifying kLastVersionNeedingMigration
and the app model id and pinned taskbar icons looked fine after upgrade.

Change-Id: Ia7f3400df8adb5b1fd9d3618f522e8f4e80b9777
Cq-Include-Trybots: luci.chromium.try:win7-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3451704
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#969739}

base/win/shortcut.cc

@@ -190,19 +190,14 @@ bool CreateOrUpdateShortcutLink(const FilePath& shortcut_path,
 
   // If we successfully created/updated the icon, notify the shell that we have
   // done so.
-  const bool succeeded = SUCCEEDED(result);
-  if (succeeded) {
-    if (shortcut_existed) {
-      // TODO(gab): SHCNE_UPDATEITEM might be sufficient here; further testing
-      // required.
-      SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, nullptr, nullptr);
-    } else {
-      SHChangeNotify(SHCNE_CREATE, SHCNF_PATH, shortcut_path.value().c_str(),
-                     nullptr);
-    }
-  }
+  if (!SUCCEEDED(result))
+    return false;
 
-  return succeeded;
+  SHChangeNotify(shortcut_existed ? SHCNE_UPDATEITEM : SHCNE_CREATE,
+                 SHCNF_PATH | SHCNF_FLUSH, shortcut_path.value().c_str(),
+                 nullptr);
+
+  return true;
 }
 
 bool ResolveShortcutProperties(const FilePath& shortcut_path,