Replace CFXJSE_HostObject::type_ with polymorphic conversion methods

More foolproof technique, and saves one word in every instance at a
cost of two pointers in every subclass vtable.

Change-Id: Ied4f91d4d203b5e6d83abe751159eb7e55489bb5
Reviewed-on: https://pdfium-review.googlesource.com/38530
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

5 files changed, 42 insertions, 29 deletions

diff --git a/fxjs/cfxjse_engine.cpp b/fxjs/cfxjse_engine.cpp
index 9b54555a21..62376dd822 100644
--- a/fxjs/cfxjse_engine.cpp
+++ b/fxjs/cfxjse_engine.cpp
@@ -77,20 +77,16 @@ CXFA_Object* CFXJSE_Engine::ToObject(
   if (!info.Holder()->IsObject())
     return nullptr;
 
-  CFXJSE_HostObject* hostObj =
+  CFXJSE_HostObject* pHostObj =
       FXJSE_RetrieveObjectBinding(info.Holder().As<v8::Object>(), nullptr);
-  if (!hostObj || hostObj->type() != CFXJSE_HostObject::kXFA)
-    return nullptr;
-  return static_cast<CXFA_Object*>(hostObj);
+  return pHostObj ? pHostObj->AsCXFAObject() : nullptr;
 }
 
 // static.
 CXFA_Object* CFXJSE_Engine::ToObject(CFXJSE_Value* pValue,
                                      CFXJSE_Class* pClass) {
   CFXJSE_HostObject* pHostObj = pValue->ToHostObject(pClass);
-  if (!pHostObj || pHostObj->type() != CFXJSE_HostObject::kXFA)
-    return nullptr;
-  return static_cast<CXFA_Object*>(pHostObj);
+  return pHostObj ? pHostObj->AsCXFAObject() : nullptr;
 }
 
 CFXJSE_Engine::CFXJSE_Engine(CXFA_Document* pDocument,
@@ -791,16 +787,12 @@ void CFXJSE_Engine::AddNodesOfRunScript(CXFA_Node* pNode) {
 }
 
 CXFA_Object* CFXJSE_Engine::ToXFAObject(v8::Local<v8::Value> obj) {
-  ASSERT(!obj.IsEmpty());
-
-  if (!obj->IsObject())
+  if (obj.IsEmpty() || !obj->IsObject())
     return nullptr;
 
-  CFXJSE_HostObject* hostObj =
+  CFXJSE_HostObject* pHostObj =
       FXJSE_RetrieveObjectBinding(obj.As<v8::Object>(), nullptr);
-  if (!hostObj || hostObj->type() != CFXJSE_HostObject::kXFA)
-    return nullptr;
-  return static_cast<CXFA_Object*>(hostObj);
+  return pHostObj ? pHostObj->AsCXFAObject() : nullptr;
 }
 
 v8::Local<v8::Value> CFXJSE_Engine::NewXFAObject(
diff --git a/fxjs/cfxjse_formcalc_context.cpp b/fxjs/cfxjse_formcalc_context.cpp
index c7433b4b2b..b0a26d86a4 100644
--- a/fxjs/cfxjse_formcalc_context.cpp
+++ b/fxjs/cfxjse_formcalc_context.cpp
@@ -450,9 +450,7 @@ bool PatternStringType(const ByteStringView& szPattern, uint32_t& patternType) {
 
 CFXJSE_FormCalcContext* ToFormCalcContext(CFXJSE_Value* pValue) {
   CFXJSE_HostObject* pHostObj = pValue->ToHostObject(nullptr);
-  if (!pHostObj || pHostObj->type() != CFXJSE_HostObject::kFM2JS)
-    return nullptr;
-  return static_cast<CFXJSE_FormCalcContext*>(pHostObj);
+  return pHostObj ? pHostObj->AsFormCalcContext() : nullptr;
 }
 
 bool IsWhitespace(char c) {
@@ -6177,15 +6175,13 @@ bool CFXJSE_FormCalcContext::Translate(const WideStringView& wsFormcalc,
     return false;
 
   wsJavascript->AppendChar(0);
-
   return !CXFA_IsTooBig(wsJavascript);
 }
 
 CFXJSE_FormCalcContext::CFXJSE_FormCalcContext(v8::Isolate* pScriptIsolate,
                                                CFXJSE_Context* pScriptContext,
                                                CXFA_Document* pDoc)
-    : CFXJSE_HostObject(kFM2JS),
-      m_pIsolate(pScriptIsolate),
+    : m_pIsolate(pScriptIsolate),
       m_pFMClass(CFXJSE_Class::Create(pScriptContext,
                                       &kFormCalcFM2JSDescriptor,
                                       false)),
@@ -6194,7 +6190,11 @@ CFXJSE_FormCalcContext::CFXJSE_FormCalcContext(v8::Isolate* pScriptIsolate,
   m_pValue.get()->SetObject(this, m_pFMClass);
 }
 
-CFXJSE_FormCalcContext::~CFXJSE_FormCalcContext() {}
+CFXJSE_FormCalcContext::~CFXJSE_FormCalcContext() = default;
+
+CFXJSE_FormCalcContext* CFXJSE_FormCalcContext::AsFormCalcContext() {
+  return this;
+}
 
 void CFXJSE_FormCalcContext::GlobalPropertyGetter(CFXJSE_Value* pValue) {
   pValue->Assign(m_pValue.get());
diff --git a/fxjs/cfxjse_formcalc_context.h b/fxjs/cfxjse_formcalc_context.h
index 052bba394a..8a92d9b0f1 100644
--- a/fxjs/cfxjse_formcalc_context.h
+++ b/fxjs/cfxjse_formcalc_context.h
@@ -25,6 +25,9 @@ class CFXJSE_FormCalcContext : public CFXJSE_HostObject {
                          CXFA_Document* pDoc);
   ~CFXJSE_FormCalcContext() override;
 
+  // CFXJSE_HostObject:
+  CFXJSE_FormCalcContext* AsFormCalcContext() override;
+
   static void Abs(CFXJSE_Value* pThis,
                   const ByteStringView& szFuncName,
                   CFXJSE_Arguments& args);
diff --git a/fxjs/fxjse.cpp b/fxjs/fxjse.cpp
new file mode 100644
index 0000000000..68adaa5dd3
--- /dev/null
+++ b/fxjs/fxjse.cpp
@@ -0,0 +1,19 @@
+// 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.
+
+// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
+
+#include "fxjs/fxjse.h"
+
+CFXJSE_HostObject::CFXJSE_HostObject() = default;
+
+CFXJSE_HostObject::~CFXJSE_HostObject() = default;
+
+CFXJSE_FormCalcContext* CFXJSE_HostObject::AsFormCalcContext() {
+  return nullptr;
+}
+
+CXFA_Object* CFXJSE_HostObject::AsCXFAObject() {
+  return nullptr;
+}
diff --git a/fxjs/fxjse.h b/fxjs/fxjse.h
index addd148117..3f2eb1d836 100644
--- a/fxjs/fxjse.h
+++ b/fxjs/fxjse.h
@@ -12,23 +12,22 @@
 #include "v8/include/v8.h"
 
 class CFXJSE_Arguments;
+class CFXJSE_FormCalcContext;
 class CFXJSE_Value;
 class CJS_Return;
+class CXFA_Object;
 
 // C++ object which is retrieved from v8 object's slot.
 class CFXJSE_HostObject {
  public:
-  virtual ~CFXJSE_HostObject() {}
+  virtual ~CFXJSE_HostObject();
 
-  // Small layering violation here, but we need to distinguish between the
-  // two kinds of subclasses.
-  enum Type { kXFA, kFM2JS };
-  Type type() const { return type_; }
+  // Two subclasses.
+  virtual CFXJSE_FormCalcContext* AsFormCalcContext();
+  virtual CXFA_Object* AsCXFAObject();
 
  protected:
-  explicit CFXJSE_HostObject(Type type) { type_ = type; }
-
-  Type type_;
+  CFXJSE_HostObject();
 };
 
 typedef CJS_Return (*FXJSE_MethodCallback)(