Step 1: Introduce a new method for source objects that will replace the current getUri

compiler/java/com/google/dart/compiler/util/DartSourceString.java

Index: compiler/java/com/google/dart/compiler/util/DartSourceString.java
===================================================================
--- compiler/java/com/google/dart/compiler/util/DartSourceString.java	(revision 5427)
+++ compiler/java/com/google/dart/compiler/util/DartSourceString.java	(working copy)
@@ -68,6 +68,15 @@
   }
 
   @Override
+  public String getUniqueIdentifier() {
+    try {
+      return new URI(null, null, getName(), null).normalize().toString();
+    } catch (URISyntaxException e) {
+      throw new IllegalArgumentException(e);
+    }
+  }
+
+  @Override
   public URI getUri() {
     try {
       return new URI(null, null, getName(), null).normalize();