Android AppRTCDemo: Add slider for changing camera capture quality during call

webrtc/examples/androidapp/res/xml/preferences.xml

 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
     <PreferenceCategory
         android:key="@string/pref_videosettings_key"
         android:title="@string/pref_videosettings_title">
 
         <CheckBoxPreference
             android:key="@string/pref_videocall_key"
             android:title="@string/pref_videocall_title"
             android:dialogTitle="@string/pref_videocall_dlg"
             android:defaultValue="@string/pref_videocall_default" />
 
         <ListPreference
             android:key="@string/pref_resolution_key"
             android:title="@string/pref_resolution_title"
             android:defaultValue="@string/pref_resolution_default"
             android:dialogTitle="@string/pref_resolution_dlg"
             android:entries="@array/videoResolutions"
             android:entryValues="@array/videoResolutionsValues" />
 
         <ListPreference
             android:key="@string/pref_fps_key"
             android:title="@string/pref_fps_title"
             android:defaultValue="@string/pref_fps_default"
             android:dialogTitle="@string/pref_fps_dlg"
             android:entries="@array/cameraFps"
             android:entryValues="@array/cameraFps" />
 
+        <CheckBoxPreference
+            android:key="@string/pref_capturequalityslider_key"
+            android:title="@string/pref_capturequalityslider_title"
+            android:dialogTitle="@string/pref_capturequalityslider_dlg"
+            android:defaultValue="@string/pref_capturequalityslider_default" />
+
         <ListPreference
             android:key="@string/pref_startvideobitrate_key"
             android:title="@string/pref_startvideobitrate_title"
             android:defaultValue="@string/pref_startvideobitrate_default"
             android:dialogTitle="@string/pref_startvideobitrate_dlg"
             android:entries="@array/startBitrate"
             android:entryValues="@array/startBitrate" />
 
         <EditTextPreference
             android:key="@string/pref_startvideobitratevalue_key"
@@ skipping 69 matching lines @@
             android:dialogTitle="@string/pref_room_server_url_dlg" />
 
         <CheckBoxPreference
             android:key="@string/pref_displayhud_key"
             android:title="@string/pref_displayhud_title"
             android:dialogTitle="@string/pref_displayhud_dlg"
            android:defaultValue="@string/pref_displayhud_default" />
     </PreferenceCategory>
 
 </PreferenceScreen>