feat(Filmstrip): Collapse filmstrip to avoid toolbar overlap on mobile

css/_variables.scss

 $newToolbarFontSize: 24px;
 $newToolbarHangupFontSize: 32px;
 $newToolbarSize: 48px;
+$newToolbarSizeMobile: 60px;
 $newToolbarSizeWithPadding: calc(#{$newToolbarSize} + 24px);
 $toolbarTitleFontSize: 19px;
 $overflowMenuItemColor: #fff;

css/filmstrip/_tile_view.scss

         display: flex;
         justify-content: center;
         align-items: center;
+        transition: margin-bottom .3s ease-in;
     }
 
     .filmstrip {
                 margin-left: $sidebarWidth;
                 width: calc(100% - #{$sidebarWidth});
 
-                .remote-videos{
+                .remote-videos {
                     width: calc(100vw - #{$sidebarWidth});
                 }
             }
         }
+
+        &.collapse {
+            #remoteVideos {
+                height: calc(100% - #{$newToolbarSizeMobile}) !important;
+                margin-bottom: $newToolbarSizeMobile;
+            }
+
+            .remote-videos {
+                // !important is needed here as overflow is set via element.style in a FixedSizeGrid.
+                overflow: hidden auto !important;
+            }
+        }
     }
 
     /**

react/features/filmstrip/components/web/Filmstrip.js

     sendAnalytics
 } from '../../../analytics';
 import { getToolbarButtons } from '../../../base/config';
+import { isMobileBrowser } from '../../../base/environment/utils';
 import { translate } from '../../../base/i18n';
 import { Icon, IconMenuDown, IconMenuUp } from '../../../base/icons';
 import { connect } from '../../../base/redux';
 import { isButtonEnabled, isToolboxVisible } from '../../../toolbox/functions.web';
 import { LAYOUTS, getCurrentLayout } from '../../../video-layout';
 import { setFilmstripVisible, setVisibleRemoteParticipants } from '../../actions';
-import { TILE_HORIZONTAL_MARGIN, TILE_VERTICAL_MARGIN, TOOLBAR_HEIGHT } from '../../constants';
+import {
+    ASPECT_RATIO_BREAKPOINT,
+    TILE_HORIZONTAL_MARGIN,
+    TILE_VERTICAL_MARGIN,
+    TOOLBAR_HEIGHT,
+    TOOLBAR_HEIGHT_MOBILE
+} from '../../constants';
 import { shouldRemoteVideosBeVisible } from '../../functions';
 
 import AudioTracksContainer from './AudioTracksContainer';
     const reduceHeight = state['features/toolbox'].visible && toolbarButtons.length;
     const remoteVideosVisible = shouldRemoteVideosBeVisible(state);
     const { isOpen: shiftRight } = state['features/chat'];
-    const className = `${remoteVideosVisible ? '' : 'hide-videos'} ${
-        reduceHeight ? 'reduce-height' : ''
-    } ${shiftRight ? 'shift-right' : ''}`.trim();
-    const videosClassName = `filmstrip__videos${visible ? '' : ' hidden'}`;
     const {
         gridDimensions = {},
         filmstripHeight,
         thumbnailSize: tileViewThumbnailSize
     } = state['features/filmstrip'].tileViewDimensions;
     const _currentLayout = getCurrentLayout(state);
+
+    const { clientHeight, clientWidth } = state['features/base/responsive-ui'];
+    const availableSpace = clientHeight - filmstripHeight;
+    let filmstripPadding = 0;
+
+    if (availableSpace > 0) {
+        const paddingValue = TOOLBAR_HEIGHT_MOBILE - availableSpace;
+
+        if (paddingValue > 0) {
+            filmstripPadding = paddingValue;
+        }
+    } else {
+        filmstripPadding = TOOLBAR_HEIGHT_MOBILE;
+    }
+
+    const collapseTileView = reduceHeight
+        && isMobileBrowser()
+        && clientWidth <= ASPECT_RATIO_BREAKPOINT;
+
+    const className = `${remoteVideosVisible ? '' : 'hide-videos'} ${
+        reduceHeight ? 'reduce-height' : ''
+    } ${shiftRight ? 'shift-right' : ''} ${collapseTileView ? 'collapse' : ''}`.trim();
+    const videosClassName = `filmstrip__videos${visible ? '' : ' hidden'}`;
     let _thumbnailSize, remoteFilmstripHeight, remoteFilmstripWidth;
 
     switch (_currentLayout) {
     case LAYOUTS.TILE_VIEW:
         _thumbnailSize = tileViewThumbnailSize;
-        remoteFilmstripHeight = filmstripHeight;
+        remoteFilmstripHeight = filmstripHeight - (collapseTileView && filmstripPadding > 0 ? filmstripPadding : 0);
         remoteFilmstripWidth = filmstripWidth;
         break;
     case LAYOUTS.VERTICAL_FILMSTRIP_VIEW: {

react/features/filmstrip/constants.js

  */
 export const TOOLBAR_HEIGHT = 72;
 
+/**
+ * The height of the whole toolbar.
+ */
+export const TOOLBAR_HEIGHT_MOBILE = 60;
+
 /**
  * The size of the horizontal border of a thumbnail.
  *