Login gaia-signin: Fit gaia dialog into webdialog

It fixes missing back button

Bug: 1000606, 1009340
Change-Id: If7839758f51f39315317cb7d8c4616ef27736295
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1829199Reviewed-by: Denis Kuznetsov <antrim@chromium.org>
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702021}

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

@@ -14,8 +14,6 @@
   display: flex;
   justify-content: center;
   left: 0;
-  /* This enables scrolling. Min resolution: 1024x768 */
-  min-height: calc(768px - var(--shelf-area-height));
   perspective: 1px; /* Workaround, see http://crbug.com/360567 */
   position: absolute;
   right: 0;

ui/login/display_manager.js

@@ -293,9 +293,11 @@ cr.define('cr.ui.login', function() {
      * @param {number} height client area height
      */
     setClientAreaSize: function(width, height) {
-      var clientArea = $('outer-container');
-      var bottom = parseInt(window.getComputedStyle(clientArea).bottom);
-      clientArea.style.minHeight = cr.ui.toCssPx(height - bottom);
+      if (!cr.isChromeOS) {
+        var clientArea = $('outer-container');
+        var bottom = parseInt(window.getComputedStyle(clientArea).bottom);
+        clientArea.style.minHeight = cr.ui.toCssPx(height - bottom);
+      }
     },
 
     /**