close external tabs on back

      Bug: 4466495
      close externally created tabs
      when the back button is used and no further
      back history is available

Change-Id: If605474d929fb759226a1e1f4125bfaab43e6653
diff --git a/src/com/android/browser/Controller.java b/src/com/android/browser/Controller.java
index 142375d..89b700b 100644
--- a/src/com/android/browser/Controller.java
+++ b/src/com/android/browser/Controller.java
@@ -2415,6 +2415,9 @@
                 // Now we close the other tab
                 closeTab(current);
             } else {
+                if ((current.getAppId() != null) || current.closeOnBack()) {
+                    closeCurrentTab();
+                }
                 /*
                  * Instead of finishing the activity, simply push this to the back
                  * of the stack and let ActivityManager to choose the foreground