Fix issue introduced by API change

Change-Id: I869f6a197721350cd2aa17be923364a901951a8a
diff --git a/src/com/android/browser/BrowserActivity.java b/src/com/android/browser/BrowserActivity.java
index 1a8e325..b882338 100644
--- a/src/com/android/browser/BrowserActivity.java
+++ b/src/com/android/browser/BrowserActivity.java
@@ -1262,6 +1262,7 @@
     @Override
     public void onActionModeStarted(ActionMode mode) {
         super.onActionModeStarted(mode);
+        mActionMode = mode;
         hideFakeTitleBar();
         // Would like to change the MENU, but onEndActionMode may not be called
         // TODO onActionModeFinished will notify when an action mode ends