[vm] Assert that we are not trying to construct old(reloaded) class constructor.

Construction of old class constructor is not possible since we didn't keep its fields, its structure.

Change-Id: I1e2239c0aa1012737e94c8ba42b0fc07a732b61d
Reviewed-on: https://dart-review.googlesource.com/c/77986
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>

runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc

@@ -1555,6 +1555,13 @@ Fragment StreamingFlowGraphBuilder::BuildFunctionBody(
   // initializers will be visible inside the entire body of the constructor.
   // We should make a separate scope for them.
   if (constructor) {
+    // PatchClass with different kernel_data means we are building a constructor
+    // for some old class. That is not supported and should not be happening as
+    // old classes are gone after hot reload, we don't have reference to old
+    // class's fields.
+    ASSERT(!Object::Handle(dart_function.RawOwner()).IsPatchClass() ||
+           (Library::Handle(Class::Handle(dart_function.Owner()).library())
+                .kernel_data() == dart_function.KernelData()));
     body += BuildInitializers(Class::Handle(Z, dart_function.Owner()));
   }