Handful of changes to get mus to shutdown correctly

components/mus/ws/platform_display.cc

Index: components/mus/ws/platform_display.cc
diff --git a/components/mus/ws/platform_display.cc b/components/mus/ws/platform_display.cc
index 4e7536e9a30619e3c866742e2fb6d69f9eacfe2c..08619e1bcf3d9afe44281965dd1a6c30db4764b7 100644
--- a/components/mus/ws/platform_display.cc
+++ b/components/mus/ws/platform_display.cc
@@ -200,7 +200,9 @@ void DefaultPlatformDisplay::Init(PlatformDisplayDelegate* delegate) {
 }
 
 DefaultPlatformDisplay::~DefaultPlatformDisplay() {
-  delegate_->OnTopLevelSurfaceChanged(cc::SurfaceId());
+  // Don't notify the delegate from the destructor.
+  delegate_ = nullptr;
+
   // Invalidate WeakPtrs now to avoid callbacks back into the
   // DefaultPlatformDisplay during destruction of |top_level_display_client_|.
   weak_factory_.InvalidateWeakPtrs();
@@ -399,7 +401,8 @@ void DefaultPlatformDisplay::OnCloseRequest() {
 }
 
 void DefaultPlatformDisplay::OnClosed() {
-  delegate_->OnDisplayClosed();
+  if (delegate_)
+    delegate_->OnDisplayClosed();
 }
 
 void DefaultPlatformDisplay::OnWindowStateChanged(