Implement 'assignToRef' resynthesizing.

pkg/analyzer/lib/src/summary/resynthesize.dart

Index: pkg/analyzer/lib/src/summary/resynthesize.dart
diff --git a/pkg/analyzer/lib/src/summary/resynthesize.dart b/pkg/analyzer/lib/src/summary/resynthesize.dart
index 749812e8812768d25825b1d6ba2808f4da24a5f5..a9505b7ce8331c37cb9bdaa4ceb27bfffd0bbb66 100644
--- a/pkg/analyzer/lib/src/summary/resynthesize.dart
+++ b/pkg/analyzer/lib/src/summary/resynthesize.dart
@@ -459,7 +459,8 @@ class _ConstExprBuilder {
         case UnlinkedConstOperation.typeCast:
         case UnlinkedConstOperation.typeCheck:
         case UnlinkedConstOperation.throwException:
-          throw new UnimplementedError('$operation');
+          _push(AstFactory.identifier3(r'$notConst$'));

[Paul Berry, 2016/05/03 19:33:41]

This seems dangerous to me, since it breaks the tracking of intPtr.  Which means
that later in the loop, we might get garbage data in our intPtr, leading to a
crash.

Since it just takes one invalid operation to render the entire constant
expression invalid, how about if we just do this instead?

return AstFactory.identifier3(r'$notConst$');

[scheglov, 2016/05/03 20:02:44]

Done.

+          break;
       }
     }
     return stack.single;