Report malformed URIs in library dependencies

pkg/compiler/lib/src/library_loader.dart

Index: pkg/compiler/lib/src/library_loader.dart
diff --git a/pkg/compiler/lib/src/library_loader.dart b/pkg/compiler/lib/src/library_loader.dart
index 3e5ddde094dd997f8b3c01f3725d8b95a6e8afd4..ab501b0133708b5c4f9a6afb348b16b6a8d1941e 100644
--- a/pkg/compiler/lib/src/library_loader.dart
+++ b/pkg/compiler/lib/src/library_loader.dart
@@ -505,7 +505,15 @@ class _LibraryLoaderTask extends CompilerTask implements LibraryLoaderTask {
                                 LibraryElement library,
                                 LibraryDependency tag) {
     Uri base = library.canonicalUri;
-    Uri resolvedUri = base.resolve(tag.uri.dartString.slowToString());
+    String tagUriString = tag.uri.dartString.slowToString();
+    Uri resolvedUri;
+    try {
+      resolvedUri = base.resolve(tagUriString);
+    } on FormatException {
+      compiler.reportError(
+          tag, MessageKind.INVALID_URI, {'uri': tagUriString});
+      return new Future.value();

[floitsch, 2015/05/06 21:19:00]

This return feels fishy.
Is the convention that this function returns a Future<null> if it couldn't load
the library? If yes, this should be part of the comment.

My guess is, that reportError was fatal and something changed.
Alternative guess is that the test's error-collector is not fatal (whereas the
dart2js one is).

In either case it's worth adding more documentation:
- add it as comment in the dartdoc.
- add a comment here: // compiler.reportError might not abort computation.

+    }
     return createLibrary(handler, library, resolvedUri, tag.uri)
         .then((LibraryElement loadedLibrary) {
           if (loadedLibrary == null) return;