Fixed compiler so that it passes Switch1NegativeTest.dart.

gen.dart

Index: gen.dart
===================================================================
--- gen.dart	(revision 839)
+++ gen.dart	(working copy)
@@ -1340,6 +1340,10 @@
       for (int i=0; i < case_.cases.length; i++) {
         var expr = case_.cases[i];
         if (expr == null) {
+          // Default can only be the last case.
+          if (i < case_.cases.length - 1) {
+            world.error('default clause must be the last case', case_.span);
+          }
           writer.writeln('default:');
         } else {
           var value = visitValue(expr);
@@ -1350,6 +1354,14 @@
       for (var stmt in case_.statements) {
         stmt.visit(this);

[jimhug, 2011/10/27 17:45:11]

This needs to do some sort of minimal checking for flow here.  In particular, we
shouldn't be adding the throw immediately after a break of a return.

[Emily Fortuna, 2011/10/27 17:59:04]

Done in the next CL.

       }
+      if (case_ != node.cases[node.cases.length - 1]) {
+        var span = case_.statements[case_.statements.length - 1].span;
+        //TODO(efortuna): This error message isn't 100% correct because 
+        // constructors are not being built correctly. Check back when I've
+        // fixed constructors. 
+        writer.writeln('\$throw(new FallThroughError("${span.file.filename}",' +
+            ' ${span.file.getLine(span.start)}))');
+      }
       writer.exitBlock('');
       _popBlock();
     }