Make some methods const in XFAJSEmbedderTest

This CL addresses the published draft comment from
https://pdfium-review.googlesource.com/c/pdfium/+/5691/

Change-Id: I7a2cd9aa5dbdde18cadb82cbef70f0e8820cc276
Reviewed-on: https://pdfium-review.googlesource.com/42871
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
diff --git a/testing/xfa_js_embedder_test.h b/testing/xfa_js_embedder_test.h
index 27dddc3..3534280 100644
--- a/testing/xfa_js_embedder_test.h
+++ b/testing/xfa_js_embedder_test.h
@@ -31,12 +31,12 @@
                                JavaScriptOption javascript_option) override;
 
   v8::Isolate* GetIsolate() const { return isolate_; }
-  CXFA_Document* GetXFADocument();
+  CXFA_Document* GetXFADocument() const;
 
   bool Execute(const ByteStringView& input);
   bool ExecuteSilenceFailure(const ByteStringView& input);
 
-  CFXJSE_Engine* GetScriptContext() { return script_context_; }
+  CFXJSE_Engine* GetScriptContext() const { return script_context_; }
   CFXJSE_Value* GetValue() const { return value_.get(); }
 
  private: