Introduce initial plumbing for type promotion in fasta.

pkg/analysis_server/analysis_server.iml

Index: pkg/analysis_server/analysis_server.iml
diff --git a/pkg/analysis_server/analysis_server.iml b/pkg/analysis_server/analysis_server.iml
index eeb9c7a6ff4077f565bd0eaa2330c2aea1b1356a..ea34ce549c3869968981b1004ea9132bb9d5c8ff 100644
--- a/pkg/analysis_server/analysis_server.iml
+++ b/pkg/analysis_server/analysis_server.iml
@@ -57,6 +57,5 @@
     <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" />

[ahe, 2017/04/24 16:47:16]

What's this for?

[Paul Berry, 2017/04/24 18:20:30]

This is one of the data files used by IntelliJ to keep track of state.  For
reasons I don't entirely understand, IntelliJ periodically messes with them. 
The changes are pretty much always benign.

If you'd rather I can extract these changes to a separate CL (or just revert
them and wait for IntelliJ to make them again in another CL).  But I find that
it's easiest to just ignore them and let IntelliJ do its thing :)

   </component>
 </module>