WebUI: restrict cr-dialogs max-height to the viewport.

ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html

Index: ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html
diff --git a/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html b/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html
index ca71e580f7eb0f2c1bc4cc1a0c89bf9393095c99..9e3018244f586dcdeadbcfa0e21a7509ddd46bcf 100644
--- a/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html
+++ b/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html
@@ -20,6 +20,20 @@
         width: 512px;
       }
 
+      :host([open]) {
+        /* Keep max-height within viewport, and flex content accordingly. */
+        display: flex;
+        flex-direction: column;
+        max-height: 100vh;
+      }
+
+      /* When needing to flex, force .body-container alone to shrink. */
+      .top-container,
+      :host ::content .button-container,
+      :host ::content .footer {
+        flex-shrink: 0;
+      }
+
       :host::backdrop {
         background-color: rgba(0, 0, 0, 0.6);
         bottom: 0;
@@ -79,6 +93,7 @@
       .body-container {
         display: flex;
         flex-direction: column;
+        min-height: 60px; /* Minimum reasonably usable height. */
         overflow: auto;
         @apply(--cr-dialog-body-container);
       }