Support sourceing files in patches.

lib/compiler/implementation/patch_parser.dart

Index: lib/compiler/implementation/patch_parser.dart
diff --git a/lib/compiler/implementation/patch_parser.dart b/lib/compiler/implementation/patch_parser.dart
index e2a2744e5a724cc2e41d6e923c065fc511b30e54..6b96677c592b3be0d805badc4c34b02dc3422503 100644
--- a/lib/compiler/implementation/patch_parser.dart
+++ b/lib/compiler/implementation/patch_parser.dart
@@ -37,7 +37,12 @@ class PatchParserTask extends leg.CompilerTask {
     // TODO(lrn): These imports end up in the original library and are in
     // scope for the original methods too. This should be fixed.
     for (tree.ScriptTag tag in imports.toLink()) {
-      compiler.scanner.importLibraryFromTag(tag, compilationUnit);
+      if (tag.isSource()) {
+        Uri resolved = patchUri.resolve(tag.argument.dartString.slowToString());
+        compiler.scanner.sourceTagInLibrary(tag, resolved, library);
+      } else {
+        compiler.scanner.importLibraryFromTag(tag, compilationUnit);
+      }
     }
   }