downloads/bookmarks: combine header CSS between downloads and bookmarks.

chrome/browser/resources/search_header.css

+/* Copyright 2014 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. */
+
+/* This is a common file for pages that have a title and search box as their
+ * header. This visually looks like:
+ * _____________________________________________________________________________
+ * |                                                                           |
+ * |  I Am So Great!                                  [ Search greatness... ]  |
+ * |___________________________________________________________________________|
+ * | Summary (90235 things currently great)                      _Great links_ |
+ *
+ * The title expands to fill any space it needs and the search bar is locked to
+ * the end of the header (e.g., right in LTR, left in RTL).
+ */
+
+header {
+  align-items: center;
+  display: flex;
+  min-width: 400px;
+  padding: 0 12px;
+}
+
+header h2 {
+  flex: 1;
+  /* TODO(dbeam): reconcile font/line-height/margin with chrome_shared.css */
+  font-size: 1.5em;
+  font-weight: normal;
+  line-height: 1;
+  margin: 15px 0;
+}
+
+header > :-webkit-any(form, input[type='search']) {
+  flex: none;
+}
+
+.summary {
+  background-color: rgb(235, 239, 249);
+  border-top: 1px solid rgb(156, 194, 239);
+  padding: 5px 10px;
+}