rn,flags: add ability to override resolution using a flag

Also, use the configured resolution to set it as the max received frame size.

react/features/app/middlewares.any.js

 import '../toolbox/middleware';
 import '../transcribing/middleware';
 import '../video-layout/middleware';
+import '../video-quality/middleware';
 import '../videosipgw/middleware';
 
 import './middleware';

react/features/base/conference/middleware.js

  */
 function _setReceiverVideoConstraint(conference, preferred, max) {
     if (conference) {
-        conference.setReceiverVideoConstraint(Math.min(preferred, max));
+        const value = Math.min(preferred, max);
+
+        conference.setReceiverVideoConstraint(value);
+        logger.info(`setReceiverVideoConstraint: ${value}`);
     }
 }
 

react/features/base/config/middleware.js

 import { jitsiLocalStorage } from 'js-utils';
 
 import { APP_WILL_MOUNT } from '../app';
+import { getFeatureFlag } from '../flags/functions';
 import { addKnownDomains } from '../known-domains';
 import { MiddlewareRegistry } from '../redux';
 import { parseURIString } from '../util';
         config.p2p = { enabled: !settings.disableP2P };
     }
 
+    const resolutionFlag = getFeatureFlag(state, 'resolution');
+
+    if (typeof resolutionFlag !== 'undefined') {
+        config.resolution = resolutionFlag;
+    }
+
     dispatch({
         type: _UPDATE_CONFIG,
         config

react/features/base/flags/constants.js

  */
 export const RECORDING_ENABLED = 'recording.enabled';
 
+/**
+ * Flag indicating the local and (maximum) remote video resolution. Overrides
+ * the server configuration.
+ * Default: (unset).
+ */
+export const RESOLUTION = 'resolution';
+
 /**
  * Flag indicating if server URL change is enabled.
  * Default: enabled (true)

react/features/conference/middleware.js

     VIDEO_QUALITY_LEVELS,
     conferenceLeft,
     getCurrentConference,
-    setPreferredVideoQuality
+    setMaxReceiverVideoQuality
 } from '../base/conference';
 import { hideDialog, isDialogOpen } from '../base/dialog';
 import { setActiveModalId } from '../base/modal';
         dispatch(setFilmstripEnabled(!reducedUI));
 
         dispatch(
-            setPreferredVideoQuality(
+            setMaxReceiverVideoQuality(
                 reducedUI
                     ? VIDEO_QUALITY_LEVELS.LOW
                     : VIDEO_QUALITY_LEVELS.HIGH));

react/features/video-layout/subscriber.js

         dispatch(selectParticipant());
 
         if (!displayTileView) {
-            dispatch(
-                setMaxReceiverVideoQuality(VIDEO_QUALITY_LEVELS.HIGH));
+            dispatch(setMaxReceiverVideoQuality(VIDEO_QUALITY_LEVELS.HIGH));
 
             if (_getAutoPinSetting()) {
                 _updateAutoPinnedParticipant(store);

react/features/video-quality/middleware.js

+// @flow
+
+import { CONFERENCE_JOINED } from '../base/conference/actionTypes';
+import { setPreferredVideoQuality } from '../base/conference/actions';
+import { MiddlewareRegistry } from '../base/redux';
+
+import logger from './logger';
+
+/**
+ * Implements the middleware of the feature video-quality.
+ *
+ * @param {Store} store - The redux store.
+ * @returns {Function}
+ */
+MiddlewareRegistry.register(({ dispatch, getState }) => next => action => {
+    const result = next(action);
+
+    switch (action.type) {
+    case CONFERENCE_JOINED: {
+        if (navigator.product === 'ReactNative') {
+            const { resolution } = getState()['features/base/config'];
+
+            if (typeof resolution !== 'undefined') {
+                dispatch(setPreferredVideoQuality(Number.parseInt(resolution, 10)));
+                logger.info(`Configured preferred receiver video frame height to: ${resolution}`);
+            }
+        }
+        break;
+    }
+    }
+
+    return result;
+});