Handle NavigableContentsFactory already bound in Assistant.

Fixes DCHECK.

Bug: b:136113743
Change-Id: I10cb6587b1017d8c734e91399b8792ab7dbd9fdc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1679063Reviewed-by: Tao Wu <wutao@chromium.org>
Commit-Queue: David Black <dmblack@google.com>
Cr-Commit-Position: refs/heads/master@{#672726}

ash/assistant/ui/assistant_web_view.cc

@@ -121,8 +121,10 @@ void AssistantWebView::OnDeepLinkReceived(
 
   RemoveContents();
 
-  delegate_->GetNavigableContentsFactoryForView(
-      contents_factory_.BindNewPipeAndPassReceiver());
+  if (!contents_factory_.is_bound()) {
+    delegate_->GetNavigableContentsFactoryForView(
+        contents_factory_.BindNewPipeAndPassReceiver());
+  }
 
   auto contents_params = content::mojom::NavigableContentsParams::New();
   contents_params->suppress_navigations = true;