Grey 'LED blink pattern' when LED Color is None

Add BooleanListPreference to allow pref_led_blink to depend on
pref_led_color being non-None.

Closes #6480

res/xml/preferences_notifications.xml

@@ -19,7 +19,7 @@
                         android:title="@string/preferences__vibrate"
                         android:summary="@string/preferences__also_vibrate_when_notified" />
 
-    <ListPreference
+    <org.thoughtcrime.securesms.preferences.BooleanListPreference
         android:key="pref_led_color"
         android:defaultValue="blue"
         android:title="@string/preferences__led_color"
@@ -31,7 +31,7 @@
         android:key="pref_led_blink"
         android:defaultValue="500,2000"
         android:title="@string/preferences__pref_led_blink_title"
-        android:dependency="pref_key_enable_notifications"
+        android:dependency="pref_led_color"
         android:entries="@array/pref_led_blink_pattern_entries"
         android:entryValues="@array/pref_led_blink_pattern_values" />
 

src/org/thoughtcrime/securesms/preferences/BooleanListPreference.java

@@ -0,0 +1,58 @@
+/**
+ * Copyright (C) 2017 Whisper Systems
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.thoughtcrime.securesms.preferences;
+
+import android.content.Context;
+import android.preference.ListPreference;
+import android.util.AttributeSet;
+
+import org.thoughtcrime.securesms.R;
+
+/**
+ * List preference that disables dependents when set to "none", similar to a CheckBoxPreference.
+ *
+ * @author Taylor Kline
+ */
+
+public class BooleanListPreference extends ListPreference {
+
+  public BooleanListPreference(Context context, AttributeSet attrs) {
+    super(context, attrs);
+  }
+
+  public BooleanListPreference(Context context) {
+    super(context);
+  }
+
+  @Override
+  public void setValue(String value) {
+    CharSequence oldEntry = getEntry();
+    super.setValue(value);
+    CharSequence newEntry = getEntry();
+    if (oldEntry != newEntry) {
+      notifyDependencyChange(shouldDisableDependents());
+    }
+  }
+
+  @Override
+  public boolean shouldDisableDependents() {
+    CharSequence newEntry = getEntry();
+    String noneEntry = getContext().getString(R.string.preferences__none);
+    boolean shouldDisable = newEntry.equals(noneEntry);
+    return shouldDisable || super.shouldDisableDependents();
+  }
+}