If a tab was opened solely to download a file, close the tab.

Fix for http://b/issue?id=2217707
diff --git a/src/com/android/browser/BrowserActivity.java b/src/com/android/browser/BrowserActivity.java
index d4a016d..b550714 100644
--- a/src/com/android/browser/BrowserActivity.java
+++ b/src/com/android/browser/BrowserActivity.java
@@ -2149,7 +2149,7 @@
         resetTitleIconAndProgress();
     }
 
-    private void goBackOnePageOrQuit() {
+    /* package */ void goBackOnePageOrQuit() {
         Tab current = mTabControl.getCurrentTab();
         if (current == null) {
             /*