Fix search box shadowing issue on classic app list.

This CL fixes a bug with the classic app list where the search box
would turn grey when typing into it. This was happening because the
shadow value from the experimental app list was being used.

BUG=469983

Review URL: https://codereview.chromium.org/1027513004

Cr-Commit-Position: refs/heads/master@{#321961}

ui/app_list/views/search_result_page_view.cc

@@ -192,7 +192,9 @@ void SearchResultPageView::OnAnimationUpdated(double progress,
 }
 
 int SearchResultPageView::GetSearchBoxZHeight() const {
-  return kSearchResultZHeight;
+  return switches::IsExperimentalAppListEnabled()
+             ? kSearchResultZHeight
+             : AppListPage::GetSearchBoxZHeight();
 }
 
 }  // namespace app_list