Second try: Fix resolution and canonicalization of typedefs and function types

runtime/vm/isolate_reload.cc

Index: runtime/vm/isolate_reload.cc
diff --git a/runtime/vm/isolate_reload.cc b/runtime/vm/isolate_reload.cc
index c375df3b8048c91b524acab028509d6a0b95a8ef..08f33dbc78c3a62aeb5224f02e7498584601b2c7 100644
--- a/runtime/vm/isolate_reload.cc
+++ b/runtime/vm/isolate_reload.cc
@@ -1596,6 +1596,9 @@ class MarkFunctionsForRecompilation : public ObjectVisitor {
     handle_ = obj;
     if (handle_.IsFunction()) {
       const Function& func = Function::Cast(handle_);
+      if (func.IsSignatureFunction()) {
+        return;
+      }
 
       // Switch to unoptimized code or the lazy compilation stub.
       func.SwitchToLazyCompiledUnoptimizedCode();