Replace header icon and illustration on migration dialog.

By the recent visual refresh on ext4 migration dialog, the header icon was
changed from chrome logo to warning icon, and the illustration was modified.

Bug: 835461
Test: Manually confirmed on Pixelbook.
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I639b7b22f21d73396f33e41af3dc8bfa084ad2de
Reviewed-on: https://chromium-review.googlesource.com/1025851Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Naoki Fukino <fukino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553494}

chrome/browser/resources/chromeos/login/encryption_migration.css

@@ -39,8 +39,12 @@ oobe-dialog > iron-icon.warning {
   --iron-icon-fill-color: rgb(219, 68, 55);
 }
 
-.chrome-logo {
-  background: url(chrome://oobe/product-logo.png) center/100% no-repeat;
+.warning-icon {
+  -webkit-mask-image: url(../../../../../ui/webui/resources/images/warning.svg);
+  -webkit-mask-position: center;
+  -webkit-mask-repeat: no-repeat;
+  -webkit-mask-size: 100%;
+  background-color: var(--google-red-500);
 }
 
 .footer {

chrome/browser/resources/chromeos/login/encryption_migration.html

@@ -25,7 +25,7 @@
     </template>
     <template is="dom-if" if="[[isReady_(uiState)]]">
       <oobe-dialog tabindex="0" has-buttons>
-        <iron-icon class="oobe-icon chrome-logo"></iron-icon>
+        <iron-icon class="oobe-icon warning-icon"></iron-icon>
         <div class="header">
           <h1 class="title">$i18n{migrationReadyTitle}</h1>
           <div class="subtitle">$i18n{migrationReadyDescription}</div>