[modules] Explicitly keep track of module requests.

src/ast/scopes.h

 // Copyright 2012 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.
 
 #ifndef V8_AST_SCOPES_H_
 #define V8_AST_SCOPES_H_
 
 #include "src/base/hashmap.h"
 #include "src/globals.h"
 #include "src/objects.h"
@@ skipping 837 matching lines @@
   // Convenience variable; function scopes only.
   Variable* arguments_;
   // Convenience variable; Subclass constructor only
   Variable* this_function_;
 };
 
 class ModuleScope final : public DeclarationScope {
  public:
   ModuleScope(DeclarationScope* script_scope,
               AstValueFactory* ast_value_factory);
+
+  // Deserialization.
+  // The generated ModuleDescriptor does not preserve all information.  In
+  // particular, its module_requests map will be empty because we no longer need
+  // the map after parsing.
   ModuleScope(Isolate* isolate, Handle<ScopeInfo> scope_info,
               AstValueFactory* ast_value_factory);
 
   ModuleDescriptor* module() const {
     DCHECK_NOT_NULL(module_descriptor_);
     return module_descriptor_;
   }
 
   // Set MODULE as VariableLocation for all variables that will live in some
   // module's export table.
   void AllocateModuleVariables();
 
  private:
   ModuleDescriptor* module_descriptor_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_SCOPES_H_