Remove React Virtualized from <Timeline>

ts/test-electron/scrollUtil_test.ts

@@ -0,0 +1,86 @@
+// Copyright 2021-2022 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+
+import {
+  getScrollBottom,
+  scrollToBottom,
+  setScrollBottom,
+} from '../util/scrollUtil';
+
+describe('scroll utilities', () => {
+  let sandbox: HTMLDivElement;
+  let el: HTMLDivElement;
+
+  // These tests to be flaky on Windows CI, sometimes timing out. That doesn't really
+  //   make sense because the test is synchronous, but this quick-and-dirty fix is
+  //   probably better than a full investigation.
+  before(function thisNeeded() {
+    if (process.platform === 'win32') {
+      this.skip();
+    }
+  });
+
+  beforeEach(() => {
+    sandbox = document.createElement('div');
+    document.body.appendChild(sandbox);
+
+    el = document.createElement('div');
+    el.innerText = 'a'.repeat(50000);
+    Object.assign(el.style, {
+      height: '50px',
+      overflow: 'scroll',
+      whiteSpace: 'wrap',
+      width: '100px',
+      wordBreak: 'break-word',
+    });
+    sandbox.appendChild(el);
+
+    assert.strictEqual(
+      el.scrollTop,
+      0,
+      'Test is not set up correctly. Element is already scrolled'
+    );
+    assert.isAtLeast(
+      el.scrollHeight,
+      50,
+      'Test is not set up correctly. scrollHeight is too low'
+    );
+  });
+
+  afterEach(() => {
+    sandbox.remove();
+  });
+
+  describe('getScrollBottom', () => {
+    it('gets the distance from the bottom', () => {
+      assert.strictEqual(
+        getScrollBottom(el),
+        el.scrollHeight - el.clientHeight
+      );
+
+      el.scrollTop = 999999;
+
+      assert.strictEqual(getScrollBottom(el), 0);
+    });
+  });
+
+  describe('setScrollBottom', () => {
+    it('sets the distance from the bottom', () => {
+      setScrollBottom(el, 12);
+      assert.strictEqual(getScrollBottom(el), 12);
+
+      setScrollBottom(el, 9999999);
+      assert.strictEqual(el.scrollTop, 0);
+    });
+  });
+
+  describe('scrollToBottom', () => {
+    it("sets the element's scrollTop to the element's scrollHeight", () => {
+      scrollToBottom(el);
+
+      assert.isAtLeast(el.scrollTop, el.scrollHeight - 50);
+    });
+  });
+});