Add screenshare support to AppRTCMobile.

webrtc/examples/androidapp/res/values/strings.xml

 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <string name="app_name" translatable="false">AppRTC</string>
     <string name="settings_name" translatable="false">AppRTC Settings</string>
     <string name="disconnect_call">Disconnect Call</string>
     <string name="room_description">
         Please enter a room name. Room names are shared with everyone, so think
         of something unique and send it to a friend.
     </string>
     <string name="favorites">Favorites</string>
@@ skipping 21 matching lines @@
     <string name="pref_room_list_key">room_list_preference</string>
 
     <string name="pref_videosettings_key">video_settings_key</string>
     <string name="pref_videosettings_title">WebRTC video settings.</string>
 
     <string name="pref_videocall_key">videocall_preference</string>
     <string name="pref_videocall_title">Video call.</string>
     <string name="pref_videocall_dlg">Enable video in a call.</string>
     <string name="pref_videocall_default">true</string>
 
+    <string name="pref_screencapture_key">screencapture_preference</string>
+    <string name="pref_screencapture_title">Use screencapture.</string>
+    <string name="pref_screencapture_default">false</string>
+
     <string name="pref_camera2_key">camera2_preference</string>
     <string name="pref_camera2_title">Use Camera2.</string>
     <string name="pref_camera2_default">true</string>
     <string name="pref_camera2_not_supported">Not supported on this device.</string>
 
     <string name="pref_resolution_key">resolution_preference</string>
     <string name="pref_resolution_title">Video resolution.</string>
     <string name="pref_resolution_dlg">Enter AppRTC local video resolution.</string>
     <string name="pref_resolution_default">Default</string>
 
@@ skipping 106 matching lines @@
     <string name="pref_displayhud_key">displayhud_preference</string>
     <string name="pref_displayhud_title">Display call statistics.</string>
     <string name="pref_displayhud_dlg">Display call statistics.</string>
     <string name="pref_displayhud_default" translatable="false">false</string>
 
     <string name="pref_tracing_key">tracing_preference</string>
     <string name="pref_tracing_title">Debug performance tracing.</string>
     <string name="pref_tracing_dlg">Debug performance tracing.</string>
     <string name="pref_tracing_default" translatable="false">false</string>
 </resources>