fix an instance of bugprone-unused-return-value

This new clang-tidy check fires when the result of a function like
`unique_ptr.release()` is unused. Sometimes this is intentional, other
times, it's not (e.g., the dev intended to `.reset()`).

Bug: 1134714
Change-Id: Ia6a272a8b45bfc3eace44d94f244cbfcedede608
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2457649Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815188}

chrome/browser/sharesheet/sharesheet_service_delegate.cc

@@ -37,7 +37,7 @@ void SharesheetServiceDelegate::ShowBubble(
 
 void SharesheetServiceDelegate::OnBubbleClosed(
     const base::string16& active_action) {
-  sharesheet_bubble_view_.release();
+  sharesheet_bubble_view_.reset();
   sharesheet_service_->OnBubbleClosed(id_, active_action);
 }