Fix debug-only crash installing app from app launcher.

chrome/browser/ui/browser.cc

Index: chrome/browser/ui/browser.cc
diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index 4dbfd458fc9c63ef00b1834aed7850bdf27100c5..b18e90f80885dc14d09781150c361f57c8df3e3e 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -1306,7 +1306,10 @@ void Browser::ShowDownload(content::DownloadItem* download) {
   // download (started before initial navigation completed) close it.
   WebContents* source = download->GetWebContents();
   if (source && source->GetController().IsInitialNavigation() &&
-      tab_strip_model_->count() > 1 && !download->IsSavePackageDownload()) {
+      tab_strip_model_->count() > 1 &&
+      tab_strip_model_->GetIndexOfWebContents(source) !=
+          TabStripModel::kNoTab &&
+      !download->IsSavePackageDownload()) {
     CloseContents(source);
   }