perf: avoid style recalc for spinner in Chrome (#2071)

src/routes/_components/LoadingSpinner.html

@@ -1,4 +1,4 @@
-<SvgIcon className="loading-spinner-icon spin {maskStyle ? 'mask-style' : ''}"
+<SvgIcon className="loading-spinner-icon {animate ? 'spin' : ''} {maskStyle ? 'mask-style' : ''}"
          style="width: {size}px; height: {size}px;"
          href="#fa-spinner"
          ariaLabel="{intl.loading}"
@@ -18,7 +18,8 @@
   export default {
     data: () => ({
       maskStyle: false,
-      size: 64
+      size: 64,
+      animate: true
     }),
     components: {
       SvgIcon

src/routes/_components/timeline/LoadingFooter.html

@@ -3,7 +3,10 @@
        aria-hidden={!showLoading}
        role="alert"
   >
-    <LoadingSpinner size={48} />
+    <!-- Sapper's mousemove event listener schedules style recalculations for the loading spinner in
+         Chrome because it's always animating, even when hidden. So disable animations when not visible
+         to avoid this. -->
+    <LoadingSpinner size={48} animate={showLoading} />
     <span class="loading-footer-info">
       {intl.loadingMore}
     </span>