Fix bad space handling in Uris.

sdk/lib/_internal/compiler/implementation/elements/modelx.dart

Index: sdk/lib/_internal/compiler/implementation/elements/modelx.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
index 78ad54785fa817a1fac5976c754e95d177c1b5c0..775841d0362a58cf764c8afc96089e453d48b575 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
@@ -971,6 +971,9 @@ class LibraryElementX extends ElementX implements LibraryElement {
    * Returns the library name (as defined by the library tag) or for script
    * (which have no library tag) the script file name. The latter case is used
    * to private 'library name' for scripts to use for instance in dartdoc.
+   *
+   * Note: the returned filename will still be escaped ("a%20b.dart" instead of
+   * "a b.dart").
    */
   String getLibraryOrScriptName() {
     if (libraryTag != null) {