Fix Tablet UI navigating unnecessarily

When the keyboard is dismissed, the browser won't navigate
unnecessarily.

Change-Id: If7d0120539cfc6db71367c549be782c58e8235dc
diff --git a/src/com/android/browser/NavigationBarBase.java b/src/com/android/browser/NavigationBarBase.java
index 48e23bd..a92090d 100644
--- a/src/com/android/browser/NavigationBarBase.java
+++ b/src/com/android/browser/NavigationBarBase.java
@@ -698,6 +698,11 @@
     @Override
     public boolean dispatchKeyEventPreIme(KeyEvent evt) {
         if (evt.getKeyCode() == KeyEvent.KEYCODE_BACK) {
+            if (mUiController.getCurrentTab() != null &&
+                    mUiController.getCurrentTab().isKeyboardShowing()){
+                stopEditingUrl();
+                return true;
+            }
             // catch back key in order to do slightly more cleanup than usual
             stopEditingUrl();
         }