Pdfium does not create isolate when it runs in chromium

BUG=pdfium:373
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/1652873003 .
diff --git a/fpdfsdk/src/fpdfview.cpp b/fpdfsdk/src/fpdfview.cpp
index ba64709..418d35d 100644
--- a/fpdfsdk/src/fpdfview.cpp
+++ b/fpdfsdk/src/fpdfview.cpp
@@ -241,7 +241,10 @@
   pModuleMgr->InitPageModule();
   pModuleMgr->InitRenderModule();
 #ifdef PDF_ENABLE_XFA
-  CPDFXFA_App::GetInstance()->Initialize();
+  CPDFXFA_App::GetInstance()->Initialize(
+      (cfg && cfg->version >= 2)
+          ? reinterpret_cast<FXJSE_HRUNTIME>(cfg->m_pIsolate)
+          : nullptr);
 #else   // PDF_ENABLE_XFA
   pModuleMgr->LoadEmbeddedGB1CMaps();
   pModuleMgr->LoadEmbeddedJapan1CMaps();