Add FlexFEC settings toggle in Android 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 71 matching lines @@
     <string name="pref_hwcodec_key">hwcodec_preference</string>
     <string name="pref_hwcodec_title">Video codec hardware acceleration.</string>
     <string name="pref_hwcodec_dlg">Use hardware accelerated video codec (if available).</string>
     <string name="pref_hwcodec_default">true</string>
 
     <string name="pref_capturetotexture_key">capturetotexture_preference</string>
     <string name="pref_capturetotexture_title">Video capture to surface texture.</string>
     <string name="pref_capturetotexture_dlg">Capture video to textures (if available).</string>
     <string name="pref_capturetotexture_default">true</string>
 
+    <string name="pref_flexfec_key">flexfec_preference</string>
+    <string name="pref_flexfec_title">Codec-agnostic Flexible FEC.</string>
+    <string name="pref_flexfec_dlg">Enable FlexFEC.</string>
+    <string name="pref_flexfec_default">false</string>
+
     <string name="pref_value_enabled">Enabled</string>
     <string name="pref_value_disabled">Disabled</string>
 
     <string name="pref_audiosettings_key">audio_settings_key</string>
     <string name="pref_audiosettings_title">WebRTC audio settings.</string>
 
     <string name="pref_startaudiobitrate_key">startaudiobitrate_preference</string>
     <string name="pref_startaudiobitrate_title">Audio bitrate setting.</string>
     <string name="pref_startaudiobitrate_dlg">Audio bitrate setting.</string>
     <string name="pref_startaudiobitrate_default">Default</string>
@@ skipping 99 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>