views/mus: Fix showing menu in chrome in mus.

For menus in chrome-in-mus, we attempt to create a Widget hosted in a native
window. For desktop builds, this means we attempt to host in a HWND or an
X11 window created by DesktopNativeWidgetAura. But for mus, we want to use
NativeWidgetMus. To do this, use the native-widget factory first if it's
available.

BUG=none

Review URL: https://codereview.chromium.org/1460003004

Cr-Commit-Position: refs/heads/master@{#361151}

base/threading/thread_restrictions.h

@@ -75,6 +75,10 @@ namespace ui {
 class WindowResizeHelperMac;
 }
 
+namespace views {
+class WindowManagerConnection;
+}
+
 namespace base {
 
 namespace android {
@@ -220,6 +224,7 @@ class BASE_EXPORT ThreadRestrictions {
   friend class ::NativeBackendKWallet;            // http://crbug.com/125331
 #if !defined(OFFICIAL_BUILD)
   friend class content::SoftwareOutputDeviceMus;  // Interim non-production code
+  friend class views::WindowManagerConnection;
 #endif
 // END USAGE THAT NEEDS TO BE FIXED.
 

chrome/browser/ui/views/chrome_views_delegate.cc

@@ -64,7 +64,6 @@
 #include "chrome/browser/ui/ash/ash_util.h"
 #endif
 
-
 // Helpers --------------------------------------------------------------------
 
 namespace {
@@ -354,6 +353,11 @@ void ChromeViewsDelegate::OnBeforeWidgetInit(
     }
   }
 #endif  // OS_WIN
+
+  if (!use_non_toplevel_window && !native_widget_factory().is_null()) {
+    params->native_widget = native_widget_factory().Run(*params, delegate);
+    return;
+  }
 #endif  // USE_AURA
 
 #if defined(OS_CHROMEOS)

ui/views/mus/window_manager_connection.cc

@@ -6,6 +6,7 @@
 
 #include "base/lazy_instance.h"
 #include "base/threading/thread_local.h"
+#include "base/threading/thread_restrictions.h"
 #include "components/mus/public/cpp/window_tree_connection.h"
 #include "components/mus/public/interfaces/window_tree.mojom.h"
 #include "mojo/application/public/cpp/application_connection.h"
@@ -111,6 +112,8 @@ mus::Window* WindowManagerConnection::NewWindow(
   window_manager_->OpenWindow(
       window_tree_client.Pass(),
       mojo::Map<mojo::String, mojo::Array<uint8_t>>::From(properties));
+
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;
   mus::WindowTreeConnection* window_tree_connection =
       mus::WindowTreeConnection::Create(
           this, window_tree_client_request.Pass(),