Gallery: Add toolbar at the top of window.

ui/file_manager/gallery/css/gallery.css

 /* Copyright (c) 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. */
 
 body {
   -webkit-user-select: none;
   font-size: 84%;
   margin: 0;
 }
 
@@ skipping 165 matching lines @@
   height: 45px;
   top: 0;
 }
 
 .gallery .header button {
   -webkit-app-region: no-drag;
 }
 
 .gallery > .toolbar {
   border-top: 1px solid rgba(50, 50, 50, 0.8);
-  bottom: 0;
   height: 55px;
   overflow: hidden;
 }
 
+.gallery > .toolbar.top {
+  top: 45px; /* Header height. */
+}
+
+.gallery > .toolbar.bottom {
+  bottom: 0;
+}
+
 .gallery[tools]:not([slideshow]) > .header,
 .gallery[tools]:not([slideshow]) > .toolbar {
   opacity: 1;
   pointer-events: auto;
 }
 
 /* Hide immediately when entering the slideshow. */
 .gallery[tools][slideshow] > .toolbar {
   transition-duration: 0ms;
 }
@@ skipping 80 matching lines @@
   pointer-events: none;
 }
 
 .gallery[tools][editing] [dimmed] {
   opacity: 0.2;
 }
 
 /* Filename */
 
 .gallery .filename-spacer {
-  flex: 0 1 auto;
+  flex: 1 0 auto;
   height: 100%;
   min-width: 140px;
   overflow: hidden;
   position: relative;
-  width: 252px;
 }
 
 .gallery .filename-spacer > * {
   background-color: transparent;
   overflow: hidden;
   position: absolute;
   transition: visibility 0ms linear 180ms, all 180ms linear;
   width: 260px;
 }
 
@@ skipping 835 matching lines @@
   padding-left: 70px;
   padding-right: 35px;
 }
 
 .gallery:not([error]) .error-banner {
   display: none;
 }
 
 /* Mosaic view. */
 .mosaic {
-  bottom: 55px;  /* Toolbar height. */
+  bottom: 0;
   left: 0;
   overflow-x: scroll;
   overflow-y: hidden;
   position: absolute;
   right: 0;
-  top: 0;
+  top: 100px; /* Header + Toolbar height. */
 
   /* transition-duration is set in Javascript. */
   transition-property: transform;
   transition-timing-function: linear;
 }
 
 .mosaic::-webkit-scrollbar {
   background: transparent;
 }
 
@@ skipping 192 matching lines @@
   background-color: rgba(255, 0, 0, 0.3);
 }
 
 .debug-me .load-target-external-metadata::before {
   background-color: rgba(0, 255, 0, 0.3);
 }
 
 .debug-me .load-target-file-entry::before {
   background-color: rgba(0, 0, 255, 0.3);
 }