feat(external_api): Add command for toggling camera on mobile web

modules/API/API.js

     pinParticipant,
     kickParticipant
 } from '../../react/features/base/participants';
+import { isToggleCameraEnabled, toggleCamera } from '../../react/features/base/tracks';
 import { setPrivateMessageRecipient } from '../../react/features/chat/actions';
 import { openChat } from '../../react/features/chat/actions.web';
 import {
             sendAnalytics(createApiEvent('film.strip.toggled'));
             APP.UI.toggleFilmstrip();
         },
+        'toggle-camera': () => {
+            if (!isToggleCameraEnabled(APP.store.getState())) {
+                return;
+            }
+
+            APP.store.dispatch(toggleCamera());
+        },
         'toggle-chat': () => {
             sendAnalytics(createApiEvent('chat.toggled'));
             APP.UI.toggleChat();

modules/API/external/external_api.js

     subject: 'subject',
     submitFeedback: 'submit-feedback',
     toggleAudio: 'toggle-audio',
+    toggleCamera: 'toggle-camera',
     toggleChat: 'toggle-chat',
     toggleFilmStrip: 'toggle-film-strip',
     toggleRaiseHand: 'toggle-raise-hand',

react/features/base/tracks/functions.js

 /* global APP */
 
+import { isMobileBrowser } from '../environment/utils';
 import JitsiMeetJS, { JitsiTrackErrors, browser } from '../lib-jitsi-meet';
 import { MEDIA_TYPE, VIDEO_TYPE, setAudioMuted } from '../media';
+import { toState } from '../redux';
 import {
     getUserSelectedCameraDeviceId,
     getUserSelectedMicDeviceId
         }
     });
 }
+
+/**
+ * Determines whether toggle camera should be enabled or not.
+ *
+ * @param {Function|Object} stateful - The redux store or {@code getState} function.
+ * @returns {boolean} - Whether toggle camera should be enabled.
+ */
+export function isToggleCameraEnabled(stateful) {
+    const state = toState(stateful);
+    const { videoInput } = state['features/base/devices'].availableDevices;
+
+    return isMobileBrowser() && videoInput.length > 1;
+}

react/features/toolbox/components/web/ToggleCameraButton.js

 // @flow
 
-import { isMobileBrowser } from '../../../base/environment/utils';
 import { translate } from '../../../base/i18n';
 import { IconCameraRefresh } from '../../../base/icons';
 import { connect } from '../../../base/redux';
 import { AbstractButton, type AbstractButtonProps } from '../../../base/toolbox/components';
-import { isLocalCameraTrackMuted, toggleCamera } from '../../../base/tracks';
+import { isLocalCameraTrackMuted, isToggleCameraEnabled, toggleCamera } from '../../../base/tracks';
 
 /**
  * The type of the React {@code Component} props of {@link ToggleCameraButton}.
 function mapStateToProps(state): Object {
     const { enabled: audioOnly } = state['features/base/audio-only'];
     const tracks = state['features/base/tracks'];
-    const { videoInput } = state['features/base/devices'].availableDevices;
 
     return {
         _audioOnly: Boolean(audioOnly),
         _videoMuted: isLocalCameraTrackMuted(tracks),
-        visible: isMobileBrowser() && videoInput.length > 1
+        visible: isToggleCameraEnabled(state)
     };
 }