Add a missing comment on a new parameter.

Filling the missing comment on the new parameter.
This also makes the paramater camelCase to be consistent.

Bug: 1040049
Test: Run existing tests
Change-Id: Icc3907675d57bb87bd55dfffe02d3e76d6460ce9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2053906Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Naoki Fukino <fukino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740996}

chrome/common/extensions/api/file_manager_private.idl

@@ -1130,10 +1130,11 @@ interface Functions {
 
   // Gets recently modified files across file systems.
   // |restriction| Flag to restrict sources of recent files.
+  // |fileType| Requested file type to filter recent files.
   // |callback|
   [nocompile]
   static void getRecentFiles(SourceRestriction restriction,
-                             RecentFileType file_type,
+                             RecentFileType fileType,
                              GetRecentFilesCallback callback);
 
   // Starts and mounts crostini container.