Create border on new browser view created by dragging out the shared tab

When dragging out the shared tab, a new browser view gets created that
doesn't have a content border yet. Create the border in this case.

Bug: 998081
Change-Id: I1aa4420adda74583461b7a78bf965dfdf0cf189a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1800746Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695994}

chrome/browser/ui/views/tab_sharing/tab_sharing_ui_views.cc

@@ -77,10 +77,15 @@ void SetContentsBorderVisible(content::WebContents* contents, bool visible) {
   Browser* browser = chrome::FindBrowserWithWebContents(contents);
   if (!browser)
     return;
+
+  BrowserView* browser_view = BrowserView::GetBrowserViewForBrowser(browser);
+  if (!browser_view->contents_border_widget()) {
+    if (!visible)
+      return;
+    InitContentsBorderWidget(contents);
+  }
   views::Widget* contents_border_widget =
-      BrowserView::GetBrowserViewForBrowser(browser)->contents_border_widget();
-  if (!contents_border_widget)
-    return;
+      browser_view->contents_border_widget();
   if (visible)
     contents_border_widget->Show();
   else