mash: Fix create fullscreen widget

Set kShowStateKey property from init params show_state so that
mus window is created properly.

BUG=714804
TEST=DesktopWindowTreeHostMusTest.CreateFullscreenWidget

Review-Url: https://codereview.chromium.org/2840903002
Cr-Commit-Position: refs/heads/master@{#467572}

ui/views/mus/desktop_window_tree_host_mus.cc

@@ -283,6 +283,8 @@ void DesktopWindowTreeHostMus::Init(aura::Window* content_window,
   content_window->SetTransparent(transparent);
   window()->SetTransparent(transparent);
 
+  window()->SetProperty(aura::client::kShowStateKey, params.show_state);
+
   if (!params.bounds.IsEmpty())
     SetBoundsInDIP(params.bounds);
 

ui/views/mus/desktop_window_tree_host_mus_unittest.cc

@@ -327,4 +327,22 @@ TEST_F(DesktopWindowTreeHostMusTest, NoShadow) {
                 wm::kShadowElevationKey));
 }
 
+TEST_F(DesktopWindowTreeHostMusTest, CreateFullscreenWidget) {
+  const Widget::InitParams::Type kWidgetTypes[] = {
+      Widget::InitParams::TYPE_WINDOW,
+      Widget::InitParams::TYPE_WINDOW_FRAMELESS,
+  };
+
+  for (auto widget_type : kWidgetTypes) {
+    Widget widget;
+    Widget::InitParams params(widget_type);
+    params.show_state = ui::SHOW_STATE_FULLSCREEN;
+    params.ownership = Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET;
+    widget.Init(params);
+
+    EXPECT_TRUE(widget.IsFullscreen())
+        << "Fullscreen creation failed for type=" << widget_type;
+  }
+}
+
 }  // namespace views