Replace Browser::GetTabContentsAt with GetWebContentsAt and update all callers.

chrome/browser/ui/panels/panel_browser_window_cocoa.mm

Index: chrome/browser/ui/panels/panel_browser_window_cocoa.mm
===================================================================
--- chrome/browser/ui/panels/panel_browser_window_cocoa.mm	(revision 116244)
+++ chrome/browser/ui/panels/panel_browser_window_cocoa.mm	(working copy)
@@ -305,12 +305,12 @@
 void PanelBrowserWindowCocoa::TabInsertedAt(TabContentsWrapper* contents,
                                             int index,
                                             bool foreground) {
-  [controller_ tabInserted:contents->tab_contents()];
+  [controller_ tabInserted:contents->web_contents()];
 }
 
 void PanelBrowserWindowCocoa::TabDetachedAt(TabContentsWrapper* contents,
                                             int index) {
-  [controller_ tabDetached:contents->tab_contents()];
+  [controller_ tabDetached:contents->web_contents()];
 }
 
 // NativePanelTesting implementation.