handle preload tab when max count is reached

       Bug: 5066968
       when opening the pre-load tab, check against max count
       if max count is already reached, replace the least
       used tab with the pre-loaded tab; it's back/forward
       history will be lost

Change-Id: I091b6b066a3e990f330be458d4aff72f62c8de38
diff --git a/src/com/android/browser/TabControl.java b/src/com/android/browser/TabControl.java
index 7055ef3..cd8da2e 100644
--- a/src/com/android/browser/TabControl.java
+++ b/src/com/android/browser/TabControl.java
@@ -514,6 +514,25 @@
         return tabsToGo;
     }
 
+    Tab getLeastUsedTab(Tab current) {
+        if (getTabCount() == 1 || current == null) {
+            return null;
+        }
+        if (mTabQueue.size() == 0) {
+            return null;
+        }
+        // find a tab which is not the current tab or the parent of the
+        // current tab
+        for (Tab t : mTabQueue) {
+            if (t != null && t.getWebView() != null) {
+                if (t != current && t != current.getParent()) {
+                    return t;
+                }
+            }
+        }
+        return null;
+    }
+
     /**
      * Show the tab that contains the given WebView.
      * @param view The WebView used to find the tab.