Fix NPE from monkey test

 Bug: 3224296

Change-Id: I3bfbb096bc29e0c6cbc6cbaad36ff0e7135b9a7c
diff --git a/src/com/android/browser/preferences/PageContentPreferencesFragment.java b/src/com/android/browser/preferences/PageContentPreferencesFragment.java
index 4bb2fab..1b5d0fe 100644
--- a/src/com/android/browser/preferences/PageContentPreferencesFragment.java
+++ b/src/com/android/browser/preferences/PageContentPreferencesFragment.java
@@ -27,6 +27,7 @@
 import android.preference.EditTextPreference;
 import android.preference.Preference;
 import android.preference.PreferenceFragment;
+import android.util.Log;
 
 public class PageContentPreferencesFragment extends PreferenceFragment
         implements Preference.OnPreferenceChangeListener {
@@ -63,6 +64,13 @@
 
     @Override
     public boolean onPreferenceChange(Preference pref, Object objValue) {
+        if (getActivity() == null) {
+            // We aren't attached, so don't accept preferences changes from the
+            // invisible UI.
+            Log.w("PageContentPreferencesFragment", "onPreferenceChange called from detached fragment!");
+            return false;
+        }
+
         if (pref.getKey().equals(BrowserSettings.PREF_HOMEPAGE)) {
             String value = (String) objValue;
             boolean needUpdate = value.indexOf(' ') != -1;