Tab Search: reduce debounce timeout value

This change makes close tab more responsive.
Since TabStripModel::CloseWebContentsAt() mostly return false,
how fast TabsChanged() is sent
to the web/js side depends on the debounce timeout value.

Bug: 1099917

Change-Id: Icd7c2a5bc45ba2b8361f8ccc5d61033ed0103462
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2335505
Commit-Queue: Yuheng Huang <yuhengh@chromium.org>
Reviewed-by: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#794353}

chrome/browser/ui/webui/tab_search/tab_search_page_handler.cc

@@ -23,7 +23,7 @@
 
 namespace {
 constexpr base::TimeDelta kTabsChangeDelay =
-    base::TimeDelta::FromMilliseconds(500);
+    base::TimeDelta::FromMilliseconds(50);
 }
 
 TabSearchPageHandler::TabSearchPageHandler(
@@ -159,6 +159,8 @@ void TabSearchPageHandler::OnTabStripModelChanged(
 void TabSearchPageHandler::TabChangedAt(content::WebContents* contents,
                                         int index,
                                         TabChangeType change_type) {
+  // TODO(crbug.com/1112496): Support more values for TabChangeType and filter
+  // out the changes we are not interested in.
   if (change_type == TabChangeType::kAll)
     ScheduleDebounce();
 }