[modules] Maintain array of cells for imports and local exports.

src/ast/modules.h

Index: src/ast/modules.h
diff --git a/src/ast/modules.h b/src/ast/modules.h
index a303c699178871e5273103ece4d8e54be27d0571..94550fb5c99b439a89855b565555e773ab228246 100644
--- a/src/ast/modules.h
+++ b/src/ast/modules.h
@@ -86,10 +86,12 @@ class ModuleDescriptor : public ZoneObject {
     int module_request;
 
     // Import/export entries that are associated with a MODULE-allocated
-    // variable use the cell_index value to encode the location of their cell.
-    // Negative values are used for imports and positive values for exports.
-    // For entries that are not associated with a MODULE-allocated variable,
-    // cell_index is 0.
+    // variable (i.e. regular_imports and regular_exports after Validate) use
+    // the cell_index value to encode the location of their cell.  During
+    // variable allocation, this will be be copied into the variable's index
+    // field.
+    // Entries that are not associated with a MODULE-allocated variable have
+    // GetCellIndexKind(cell_index) == kInvalid.
     int cell_index;
 
     // TODO(neis): Remove local_name component?
@@ -109,6 +111,9 @@ class ModuleDescriptor : public ZoneObject {
                               Handle<ModuleInfoEntry> entry);
   };
 
+  enum CellIndexKind { kInvalid, kExport, kImport };
+  static CellIndexKind GetCellIndexKind(int cell_index);
+
   // Module requests.
   const ZoneMap<const AstRawString*, int>& module_requests() const {
     return module_requests_;