MD Downloads: use "big search" box like MD history

chrome/browser/resources/md_downloads/manager.css

 /* Copyright 2015 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. */
 
 :host {
   display: flex;
   flex: 1 0;
   flex-direction: column;
   height: 100%;
-  overflow-y: overlay;
 }
 
 @media screen and (max-width: 1024px) {
   :host {
     flex-basis: 670px;  /* 622 card width + 24 left margin + 24 right margin. */
   }
 }
 
+#downloads-list {
+  /* TODO(dbeam): we're not setting scrollTarget explicitly, yet
+   * style="overflow: auto" is still being set by <iron-list>'s JS. Weird. */
+  overflow-y: overlay !important;
+}
+
 #no-downloads,
 #downloads-list {
   flex: 1;
 }
 
 :host([loading]) #no-downloads,
 :host([loading]) #downloads-list {
   display: none;
 }
 
 #no-downloads {
   align-items: center;
   color: #b4b4b4;
   display: flex;
   font-size: 123.1%;
   font-weight: 500;
   justify-content: center;
   /* To avoid overlapping with the header, we need this min-height
    * until bug 596743 is fixed. */
   min-height: min-content;
 }
 
 #no-downloads .illustration {
   background: -webkit-image-set(
       url(chrome://downloads/1x/no_downloads.png) 1x,
       url(chrome://downloads/2x/no_downloads.png) 2x) no-repeat center center;
   height: 144px;  /* Matches natural image height. */
   margin-bottom: 32px;
 }