Support for Signal calls.

Merge in RedPhone

// FREEBIE

res/drawable/redphone_btn_compound_mute.xml

@@ -0,0 +1,30 @@
+<?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.
+-->
+
+<!-- Layers used to render the in-call "Mute" compound button. -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <!-- The standard "compound button" background. -->
+    <item android:drawable="@drawable/redphone_btn_compound_background" />
+
+    <!-- ...and the actual icon on top.  Use an explicit <bitmap> to avoid scaling
+         the icon up to the full size of the button. -->
+    <item>
+        <bitmap android:src="@drawable/redphone_ic_mute_holo_dark"
+                android:gravity="center" />
+    </item>
+
+</layer-list>