[MD History] Add shadow to toolbar on scroll.

chrome/browser/resources/md_history/app.vulcanized.html

Index: chrome/browser/resources/md_history/app.vulcanized.html
diff --git a/chrome/browser/resources/md_history/app.vulcanized.html b/chrome/browser/resources/md_history/app.vulcanized.html
index 71ff6528505144cf2358d4f85b702836841f163d..4109a83a5af7589a1e61a75b89baa1cc4a119952 100644
--- a/chrome/browser/resources/md_history/app.vulcanized.html
+++ b/chrome/browser/resources/md_history/app.vulcanized.html
@@ -3545,6 +3545,8 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
     </div>
     </template>
   </dom-module>
+
+
 <dom-module id="iron-list" assetpath="chrome://resources/polymer/v1_0/iron-list/">
   <template>
     <style>
@@ -3968,6 +3970,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
        * crbug.com/618153. TODO(dbeam): is this still an issue? */
       #main-container {
         height: calc(100% - var(--toolbar-height));
+        position: relative;
       }
 
       :host([grouped_]) #main-container {
@@ -4001,6 +4004,22 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
         font-size: 123%;
         font-weight: 400;
       }
+
+      #drop-shadow {
+        box-shadow: inset 0 5px 6px -3px rgba(0, 0, 0, 0.4);
+        height: 6px;
+        left: 0;
+        opacity: 0;
+        pointer-events: none;
+        position: absolute;
+        right: 0;
+        top: 0;
+        transition: opacity 500ms;
+      }
+
+      :host([toolbar-shadow_]) #drop-shadow {
+        opacity: 1;
+      }
     </style>
     <app-location route="{{route_}}"></app-location>
     <app-route route="{{route_}}" pattern="/:page" data="{{routeData_}}" query-params="{{queryParams_}}">
@@ -4021,6 +4040,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
           </history-synced-device-manager>
         </template>
       </iron-pages>
+      <div id="drop-shadow"></div>
     </div>
 
     <template is="dom-if" if="[[hasDrawer_]]">