Tab Search: Ensure cached WebContents starts rendering when reloaded

A cached WebView's WebContents in WebUIBubbleManager may not
necessarily be in a visible state that enables processing of
rendering events.

Call WasShown() before reloading to ensure the WebContents propagates
these events and ShowUI() is eventually called.

Bug: None
Change-Id: I810b2e10e286e8cca1948ee6aab014efa843db86
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2530192Reviewed-by: Peter Boström <pbos@chromium.org>
Commit-Queue: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826148}

chrome/browser/ui/views/bubble/webui_bubble_manager.cc

@@ -40,6 +40,10 @@ bool WebUIBubbleManagerBase::ShowBubble() {
   cache_timer_->Stop();
 
   if (cached_web_view_) {
+    // The cached WebView's WebContents may not necessarily be in a visible
+    // state. Lie to WebContents so it starts rendering and eventually calls
+    // ShowUI().
+    cached_web_view_->GetWebContents()->WasShown();
     cached_web_view_->GetWebContents()->ReloadFocusedFrame();
     bubble_using_cached_webview_ = true;
   } else {