Fix another assertion in the context typer.

src/compiler/typer.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/graph-inl.h"
 #include "src/compiler/js-operator.h"
 #include "src/compiler/node.h"
 #include "src/compiler/node-properties-inl.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/simplified-operator.h"
@@ skipping 77 matching lines @@
   VALUE_OP_LIST(DECLARE_METHOD)
 #undef DECLARE_METHOD
 
   Bounds OperandType(Node* node, int i) {
     return NodeProperties::GetBounds(NodeProperties::GetValueInput(node, i));
   }
 
   Type* ContextType(Node* node) {
     Bounds result =
         NodeProperties::GetBounds(NodeProperties::GetContextInput(node));
-    DCHECK(result.upper->Is(Type::Internal()));
-    DCHECK(result.lower->Equals(result.upper));
+    DCHECK(result.upper->Maybe(Type::Internal()));
+    // TODO(rossberg): More precisely, instead of the above assertion, we should
+    // back-propagate the constraint that it has to be a subtype of Internal.
     return result.upper;
   }
 
   Zone* zone() { return typer_->zone(); }
   Isolate* isolate() { return typer_->isolate(); }
   MaybeHandle<Context> context() { return context_; }
 
  private:
   Typer* typer_;
   MaybeHandle<Context> context_;
@@ skipping 738 matching lines @@
 }
 
 
 void Typer::DecorateGraph(Graph* graph) {
   graph->AddDecorator(new (zone()) TyperDecorator(this));
 }
 
 }
 }
 }  // namespace v8::internal::compiler