Add Mic Toggle button to AppRTCDemo (Android).

webrtc/examples/androidapp/res/layout/fragment_call.xml

 <?xml version="1.0" encoding="utf-8"?>
 
 <RelativeLayout
         xmlns:android="http://schemas.android.com/apk/res/android"
         xmlns:tools="http://schemas.android.com/tools"
         android:layout_width="match_parent"
         android:layout_height="match_parent">
 
     <TextView
         android:id="@+id/contact_name_call"
@@ skipping 29 matching lines @@
            android:layout_marginEnd="8dp"
            android:layout_width="48dp"
            android:layout_height="48dp"/>
 
         <ImageButton
            android:id="@+id/button_call_scaling_mode"
            android:background="@drawable/ic_action_return_from_full_screen"
            android:contentDescription="@string/disconnect_call"
            android:layout_width="48dp"
            android:layout_height="48dp"/>
+
+       <ImageButton
+           android:id="@+id/button_call_toggle_mic"
+           android:background="@android:drawable/ic_btn_speak_now"
+           android:contentDescription="@string/toggle_mic"
+           android:layout_marginEnd="8dp"
+           android:layout_width="48dp"
+           android:layout_height="48dp"/>
     </LinearLayout>
 
     <TextView
         android:id="@+id/capture_format_text_call"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_centerHorizontal="true"
         android:layout_above="@+id/capture_format_slider_call"
         android:textSize="16sp"
         android:text="Slide to change capture format"/>
 
     <SeekBar
         android:id="@+id/capture_format_slider_call"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_centerHorizontal="true"
         android:layout_alignParentBottom="true"
         android:progress="50"
         android:layout_margin="8dp"/>
 
 </RelativeLayout>