[Chromecast] Fix CastWebViewDefault crash

Don't initialize the underlying window if it has already been destroyed.

Bug: internal b/144003508
Test: CQ
Change-Id: Ic18a8f8c81e2bebf05e757b215f04e6d3ed5b9f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917684
Auto-Submit: Sean Topping <seantopping@chromium.org>
Commit-Queue: Simeon Anfinrud <sanfin@chromium.org>
Reviewed-by: Simeon Anfinrud <sanfin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715762}

chromecast/browser/cast_web_view_default.cc

@@ -123,7 +123,8 @@ void CastWebViewDefault::CloseContents(content::WebContents* source) {
 
 void CastWebViewDefault::InitializeWindow(mojom::ZOrder z_order,
                                           VisibilityPriority initial_priority) {
-  DCHECK(window_);
+  if (!window_)
+    return;
   window_->CreateWindowForWebContents(&cast_web_contents_, z_order,
                                       initial_priority);
   web_contents_->Focus();