Navigation buttons should not enable if user can not navigate

content/shell/android/java/src/org/chromium/content_shell/Shell.java

 // Copyright 2012 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.content_shell;
 
 import android.content.Context;
 import android.graphics.drawable.ClipDrawable;
 import android.text.TextUtils;
 import android.util.AttributeSet;
@@ skipping 250 matching lines @@
         if (mContentViewCore.getUrl() != null) mUrlTextView.setText(mContentViewCore.getUrl());
         ((FrameLayout) findViewById(R.id.contentview_holder)).addView(cv,
                 new FrameLayout.LayoutParams(
                         FrameLayout.LayoutParams.MATCH_PARENT,
                         FrameLayout.LayoutParams.MATCH_PARENT));
         cv.requestFocus();
         mContentViewRenderView.setCurrentContentViewCore(mContentViewCore);
     }
 
     /**
+     * Enable/Disable navigation(Prev/Next) button if navigation is allowed/disallowed
+     * in respective direction.
+     * @param controlId Id of button to update
+     * @param enabled enable/disable value
+     */
+    @CalledByNative
+    private void enableUiControl(int controlId, boolean enabled) {
+        if (controlId == 0) mPrevButton.setEnabled(enabled);
+        else if (controlId == 1) mNextButton.setEnabled(enabled);
+    }
+
+    /**
      * @return The {@link ViewGroup} currently shown by this Shell.
      */
     public ViewGroup getContentView() {
         return mContentViewCore.getContainerView();
     }
 
     /**
      * @return The {@link ContentViewCore} currently managing the view shown by this Shell.
      */
     public ContentViewCore getContentViewCore() {
         return mContentViewCore;
     }
 
     private void setKeyboardVisibilityForUrl(boolean visible) {
         InputMethodManager imm = (InputMethodManager) getContext().getSystemService(
                 Context.INPUT_METHOD_SERVICE);
         if (visible) {
             imm.showSoftInput(mUrlTextView, InputMethodManager.SHOW_IMPLICIT);
         } else {
             imm.hideSoftInputFromWindow(mUrlTextView.getWindowToken(), 0);
         }
     }
 
     private static native void nativeCloseShell(long shellPtr);
 }