Cleanup temporary incognito mode files after last tab closes.

Change-Id: Ia685fb162d7449d2cd850e87607eff39cc8893a5
diff --git a/src/com/android/browser/BrowserActivity.java b/src/com/android/browser/BrowserActivity.java
index b62862b..24796a6 100644
--- a/src/com/android/browser/BrowserActivity.java
+++ b/src/com/android/browser/BrowserActivity.java
@@ -2086,6 +2086,10 @@
         mTabControl.setCurrentTab(mTabControl.getTab(currentIndex));
         resetTitleIconAndProgress();
         updateLockIconToLatest();
+
+        if (!mTabControl.hasAnyOpenIncognitoTabs()) {
+            WebView.cleanupPrivateBrowsingFiles(this);
+        }
     }
 
     /* package */ void goBackOnePageOrQuit() {