Avoid passing a null uri to translateUri.

lib/compiler/implementation/compiler.dart

 // Copyright (c) 2012, 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.
 
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
 final bool REPORT_EXCESS_RESOLUTION = false;
@@ skipping 350 matching lines @@
                      api.Diagnostic.CRASH);
     // TODO(ahe): Obtain the build ID.
     var buildId = 'build number could not be determined';
     print(MessageKind.PLEASE_REPORT_THE_CRASH.message([buildId]));
   }
 
   void cancel([String reason, Node node, Token token,
                HInstruction instruction, Element element]) {
     assembledCode = null; // Compilation failed. Make sure that we
                           // don't return a bogus result.
-    SourceSpan span = const SourceSpan(null, null, null);
+    SourceSpan span = null;
     if (node !== null) {
       span = spanFromNode(node);
     } else if (token !== null) {
       span = spanFromTokens(token, token);
     } else if (instruction !== null) {
       span = spanFromElement(currentElement);
     } else if (element !== null) {
       span = spanFromElement(element);
     } else {
       throw 'No error location for error: $reason';
@@ skipping 502 matching lines @@
     // invariant that endOffset > beginOffset, but for EOF the
     // charoffset of the next token may be [beginOffset]. This can
     // also happen for synthetized tokens that are produced during
     // error handling.
     final endOffset =
       Math.max((end.next !== null) ? end.next.charOffset : 0, beginOffset + 1);
     assert(endOffset > beginOffset);
     return f(beginOffset, endOffset);
   }
 }