downloads: add "No downloads" and "No search results" messages.

chrome/browser/resources/downloads/downloads.css

 /* Copyright (c) 2012 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. */
 
 <include src="../search_header.css">
 
 #downloads-summary-text {
   font-weight: bold;
 }
 
 .disabled-link {
   color: #999;
   text-decoration: none;
 }
 
 #downloads-actions > a,
 #downloads-actions > .disabled-link {
   -webkit-margin-start: 10px;
 }
 
 #downloads-actions > a:first-child {
   -webkit-margin-start: 0;
 }
 
 #open-downloads-folder {
   -webkit-margin-end: 16px;
 }
 
-#downloads-display {
+#downloads-display,
+#no-downloads-or-results {
   max-width: 740px;
   padding: 0 10px 34px;
 }
 
 .download {
   -webkit-margin-start: 114px;
-  -webkit-padding-start: 56px;
+  -webkit-padding-start: 52px;
   margin-bottom: 15px;
+  position: relative;
+}
+
+.download,
+#no-downloads-or-results {
   margin-top: 6px;
-  position: relative;
 }
 
 .date-container {
   left: -110px;
   position: absolute;
   width: 110px;
 }
 
 html[dir=rtl] .date-container {
   left: auto;
@@ skipping 54 matching lines @@
 html[dir=rtl] .progress {
   left: auto;
   right: 0;
 }
 
 .progress.background {
   background: url('chrome://theme/IDR_DOWNLOAD_PROGRESS_BACKGROUND_32');
   background-size: 48px;
 }
 
+.name,
+.src-url,
+.controls a {
+  -webkit-padding-end: 4px;
+  -webkit-padding-start: 4px;
+}
+
 .name {
   -webkit-padding-end: 16px;
   display: none;
   max-width: 450px;
   word-break: break-all;
 }
 
 .interrupted {
   color: red;
 }
 
 .download .status {
   color: #999;
   white-space: nowrap;
 }
 
 .download .src-url {
   color: rgb(85, 102, 221);
   display: inline-block;
   max-width: 500px;
   overflow: hidden;
   padding-bottom: 1px;
   padding-top: 4px;
   text-decoration: none;
   text-overflow: ellipsis;
   white-space: nowrap;
 }
 
 .controls a {
-  -webkit-margin-end: 16px;
+  -webkit-margin-end: 12px;
   color: #777;
 }
 
 #downloads-pagination {
   -webkit-margin-start: 18px;
   padding-top: 24px;
 }