Navigation buttons should not enable if user can not navigate

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

Index: content/shell/android/java/src/org/chromium/content_shell/Shell.java
diff --git a/content/shell/android/java/src/org/chromium/content_shell/Shell.java b/content/shell/android/java/src/org/chromium/content_shell/Shell.java
index 9e01a9df7abfab800e63c719bd8899d005c53dec..2b63bc0273f7b3d3d7eb7982adbfc9fae9e3f297 100644
--- a/content/shell/android/java/src/org/chromium/content_shell/Shell.java
+++ b/content/shell/android/java/src/org/chromium/content_shell/Shell.java
@@ -268,6 +268,18 @@ public class Shell extends LinearLayout {
     }
 
     /**
+     * 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() {