Ensure usage of short form (e.g. dart:io rather than dart://io/io_runtime.dart) if available

compiler/java/com/google/dart/compiler/DefaultCompilerConfiguration.java

Index: compiler/java/com/google/dart/compiler/DefaultCompilerConfiguration.java
===================================================================
--- compiler/java/com/google/dart/compiler/DefaultCompilerConfiguration.java	(revision 6094)
+++ compiler/java/com/google/dart/compiler/DefaultCompilerConfiguration.java	(working copy)
@@ -114,6 +114,13 @@
     if( null == this.systemLibraryManager.expandRelativeDartUri(systemUri) ) {
       return null;
     }
+
+    // Ensure we are using the short form if it exists
+    URI shortUri = systemLibraryManager.getShortUri(systemUri);
+    if (shortUri != null) {
+      systemUri = shortUri;
+    }
+
     return new UrlLibrarySource(systemUri, this.systemLibraryManager);
   }