Always build JS Runtime stubs even if V8 present.

Prerequisite for switching V8 off at run-time.

Change-Id: I4b9f867185758350f5de3f57e771f63020df6e65
Reviewed-on: https://pdfium-review.googlesource.com/30994
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
diff --git a/fxjs/ijs_runtime.cpp b/fxjs/ijs_runtime.cpp
new file mode 100644
index 0000000..03538cd
--- /dev/null
+++ b/fxjs/ijs_runtime.cpp
@@ -0,0 +1,38 @@
+// Copyright 2018 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "fxjs/ijs_runtime.h"
+
+#include "fpdfsdk/cpdfsdk_helpers.h"
+#include "fxjs/cjs_runtimestub.h"
+#include "third_party/base/ptr_util.h"
+
+#ifdef PDF_ENABLE_V8
+#include "fxjs/cfxjs_engine.h"
+#include "fxjs/cjs_runtime.h"
+#endif
+
+// static
+void IJS_Runtime::Initialize(unsigned int slot, void* isolate) {
+#ifdef PDF_ENABLE_V8
+  FXJS_Initialize(slot, reinterpret_cast<v8::Isolate*>(isolate));
+#endif
+}
+
+// static
+void IJS_Runtime::Destroy() {
+#ifdef PDF_ENABLE_V8
+  FXJS_Release();
+#endif
+}
+
+// static
+std::unique_ptr<IJS_Runtime> IJS_Runtime::Create(
+    CPDFSDK_FormFillEnvironment* pFormFillEnv) {
+#ifdef PDF_ENABLE_V8
+  return pdfium::MakeUnique<CJS_Runtime>(pFormFillEnv);
+#else
+  return pdfium::MakeUnique<CJS_RuntimeStub>(pFormFillEnv);
+#endif
+}