Revert the patch that has disabled Panels for M53 (https://codereview.chromium.org/2083113002)

chrome/browser/ui/panels/panel_manager.cc

Index: chrome/browser/ui/panels/panel_manager.cc
diff --git a/chrome/browser/ui/panels/panel_manager.cc b/chrome/browser/ui/panels/panel_manager.cc
index 3ae9d5c8287c2751cc54f5ae65038b1e88bd9066..7d2c9cec5a78d650b69545e879eab81a9327f98c 100644
--- a/chrome/browser/ui/panels/panel_manager.cc
+++ b/chrome/browser/ui/panels/panel_manager.cc
@@ -131,16 +131,11 @@ bool PanelManager::ShouldUsePanels(const std::string& extension_id) {
   }
 #endif  // USE_X11 && !OS_CHROMEOS
 
-// Panels are an Eraser target. See http://crbug.com/571511 for details.
-// TODO(dimich): remove the rest of Panels code (except ChromeOS) once
-// erasure is stable.
-#if defined(OS_CHROMEOS)
-  // Without --enable-panels, only support Hangouts on ChromeOS.
+  // Without --enable-panels, only support Hangouts.
   for (const char* id : extension_misc::kHangoutsExtensionIds) {
     if (extension_id == id)
       return true;
   }
-#endif  // OS_CHROMEOS
 
   return false;
 }