Support for Signal calls.

Merge in RedPhone

// FREEBIE

res/drawable/redphone_ic_lockscreen_answer.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2011 The Android Open Source Project
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+<selector xmlns:android="http://schemas.android.com/apk/res/android"
+          android:constantSize="true">
+
+    <item
+        android:state_enabled="true"
+        android:state_active="false"
+        android:state_focused="false"
+        android:drawable="@drawable/redphone_ic_lockscreen_answer_normal" />
+
+    <item
+        android:state_enabled="true"
+        android:state_active="true"
+        android:state_focused="false"
+        android:drawable="@drawable/redphone_ic_lockscreen_answer_active" />
+
+</selector>