Tab manager view should hide on press of back key

chrome/android/shell/java/src/org/chromium/chrome/shell/TabManager.java

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.shell;
 
 import android.content.Context;
 import android.util.AttributeSet;
 import android.view.View;
 import android.view.ViewGroup;
@@ skipping 172 matching lines @@
         contentViewCore.onShow();
     }
 
     /**
      * Toggles the tab switcher visibility.
      */
     public void toggleTabSwitcher() {
         mTabModelSelector.toggleTabSwitcher();
     }
 
+    public boolean isTabSwitcherVisible() {
+        return mTabModelSelector.isTabSwitcherVisible();
+    }
+
+    public void hideTabSwitcher() {
+        mTabModelSelector.hideTabSwitcher();
+    }
+
     /**
      * Opens a URL in the current tab if one exists, or in a new tab otherwise.
      * @param url The URL to open.
      * @return The tab used to open the provided URL.
      */
     public Tab openUrl(String url) {
         LoadUrlParams loadUrlParams = new LoadUrlParams(url);
         loadUrlParams.setTransitionType(PageTransition.TYPED | PageTransition.FROM_ADDRESS_BAR);
         Tab tab = mTabModelSelector.getCurrentTab();
         if (tab != null) {
             tab.loadUrl(loadUrlParams);
             return tab;
         }
         return createTab(url, TabLaunchType.FROM_KEYBOARD);
     }
 }