code: private void maybeAddImportedFileReferenceToSymbolTable(
        Node importStringNode, String importedFilePath) {
      if (preprocessorSymbolTable == null) {
        return;
      }
  
      // If this if the first import that mentions importedFilePath then we need to create a SCRIPT
      // node for the imported file.
      if (preprocessorSymbolTable.getSlot(importedFilePath) == null) {
        Node scriptNode = compiler.getScriptNode(importedFilePath);
        if (scriptNode != null) {
          preprocessorSymbolTable.addReference(scriptNode, importedFilePath);
        }
      }
  
      preprocessorSymbolTable.addReference(importStringNode, importedFilePath);
    }
docs: Add reference to a file that current module imports. Example:
  
  <pre>
  import * as qux from '../some/file.js';
  </pre>
  
  <p>Will add a reference to file.js on the string node `'../some/file.js'`.
  
  @param importStringNode String node from the import statement that references imported file. In
  the example above it is the '../some/file.js' STRING node.
  @param importedFilePath Absolute path to the imported file. In the example above it can be
  myproject/folder/some/file.js