Change accessors and AstFactory to use tokens rather than file offsets.

pkg/front_end/front_end.iml

Index: pkg/front_end/front_end.iml
diff --git a/pkg/front_end/front_end.iml b/pkg/front_end/front_end.iml
index b515edb8df87bb138656c9dbbd32e9b03b4b2b4a..88e7b04e082de99c2219cf0392389791ad3ee50e 100644
--- a/pkg/front_end/front_end.iml
+++ b/pkg/front_end/front_end.iml
@@ -9,6 +9,7 @@
       <excludeFolder url="file://$MODULE_DIR$/test/fasta/packages" />
       <excludeFolder url="file://$MODULE_DIR$/test/fasta/parser/packages" />
       <excludeFolder url="file://$MODULE_DIR$/test/fasta/scanner/packages" />
+      <excludeFolder url="file://$MODULE_DIR$/test/fasta/type_inference/packages" />
       <excludeFolder url="file://$MODULE_DIR$/test/packages" />
       <excludeFolder url="file://$MODULE_DIR$/test/src/base/packages" />
       <excludeFolder url="file://$MODULE_DIR$/test/src/packages" />
@@ -19,6 +20,5 @@
     <orderEntry type="sourceFolder" forTests="false" />
     <orderEntry type="library" name="Dart SDK" level="application" />
     <orderEntry type="library" name="Dart SDK" level="project" />
-    <orderEntry type="library" name="Dart Packages" level="project" />
   </component>
 </module>