DevTools: Introduce Landing page for Timeline panel.

third_party/WebKit/Source/devtools/front_end/timeline/timelineLandingPage.css

+/*
+ * Copyright (c) 2016 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+.timeline-landing-page {
+    align-self: center;
+    max-width: 500px;
+    font-size: 13px;
+}
+
+.timeline-landing-page .tabbed-pane {
+    padding: 10px 0 0 0;
+}
+
+.timeline-landing-page .timeline-perspective-body {
+    align-items: stretch;
+    line-height: 1.5;
+    padding: 12px;
+    white-space: pre-line;
+    width: 100%;
+    font-size: 12px;
+}
+
+.timeline-landing-page .timeline-perspective-body > div {
+    margin-bottom: 12px;
+    flex-shrink: 0;
+}
+
+.timeline-landing-page button {
+    width: 90px;

[caseq, 2016/12/12 19:04:34]

let's not do that, it's a landmine.

[alph, 2016/12/12 20:43:13]

I need to specify width to make sure all the [potential] buttons have the same
size. Though I can make it less painful, by using min-width.

+    height: 26px;
+    margin: 10px 0 0 0;
+}
+
+.timeline-landing-page .recording-setting {
+    display: flex;
+    align-items: flex-start;
+    margin-bottom: 2px !important;
+}
+
+.timeline-landing-page .recording-setting label {
+    flex: 100px 0 0;

[caseq, 2016/12/12 19:04:34]

we typically put basis at the end of the shorthand.

[alph, 2016/12/12 20:43:13]

Indeed. There are 60 instances vs 14.

+}
+
+.timeline-landing-page .recording-setting-description {
+    color: #999;
+}