Properly resolve relative paths with spaces

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 5115)
+++ compiler/java/com/google/dart/compiler/util/DartSourceString.java	(working copy)
@@ -10,6 +10,7 @@
 import java.io.Reader;
 import java.io.StringReader;
 import java.net.URI;
+import java.net.URISyntaxException;
 
 /**
  * Instances of the class <code>DartSourceString</code> represent a source
@@ -68,6 +69,10 @@
 
   @Override
   public URI getUri() {
-    return URI.create(getName()).normalize();
+    try {
+      return new URI(null, null, getName(), null).normalize();
+    } catch (URISyntaxException e) {
+      throw new IllegalArgumentException(e);
+    }
   }
 }