Step one towards stable error messages with details:

pkg/polymer/lib/src/build/log_injector.css

 /** Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
     for details. All rights reserved. Use of this source code is governed by a
     BSD-style license that can be found in the LICENSE file. **/
 .build-logs {
   position: fixed;
   bottom: 0;
   right: 0;
-  max-width: 50vw;
+  max-width: 80vw;
   z-index: 10000;
   font-family: sans-serif !important;
 }
 .build-logs .log {
   padding: 0.6em;
   background: black;
   color: white;
   border: solid 1px #666;
   border-bottom: 0px;
+  text-overflow: ellipsis;
+  overflow-x: hidden;
 }
 .build-logs .fine {
   color: green;
 }
 .build-logs .info {
   color: yellow;
 }
 .build-logs .warning {
   color: orange;
 }
 .build-logs .error {
   color: red;
 }
 .build-logs .message {
   white-space: nowrap;
-  text-overflow: ellipsis;
-  overflow-x: hidden;
   cursor: pointer;
 }
 .build-logs .message.expanded {
   white-space: normal;
 }
 .build-logs .message a {
   color: #CCF;
   text-decoration: bold;
 }
 .build-logs .menu {
@@ skipping 24 matching lines @@
 .build-logs .content > div.active {
   display: block;
 }
 
 .build-logs .content span.text {
   padding: 0.4em 0.2em 0.2em 2em;
   white-space: pre;
   display: block;
   font-family: monospace !important;
 }