Return v8::Date specialization not v8::Value where possible

fxjs/include/fxjs_v8.h

 // Copyright 2014 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
 
 // FXJS_V8 is a layer that makes it easier to define native objects in V8, but
 // has no knowledge of PDF-specific native objects. It could in theory be used
 // to implement other sets of native objects.
 
@@ skipping 242 matching lines @@
                               unsigned index,
                               v8::Local<v8::Value> pValue);
 
 v8::Local<v8::Value> FXJS_NewNull(v8::Isolate* pIsolate);
 v8::Local<v8::Array> FXJS_NewArray(v8::Isolate* pIsolate);
 v8::Local<v8::Value> FXJS_NewNumber(v8::Isolate* pIsolate, int number);
 v8::Local<v8::Value> FXJS_NewNumber(v8::Isolate* pIsolate, double number);
 v8::Local<v8::Value> FXJS_NewNumber(v8::Isolate* pIsolate, float number);
 v8::Local<v8::Value> FXJS_NewBoolean(v8::Isolate* pIsolate, bool b);
 v8::Local<v8::Value> FXJS_NewString(v8::Isolate* pIsolate, const wchar_t* str);
-v8::Local<v8::Value> FXJS_NewDate(v8::Isolate* pIsolate, double d);
+v8::Local<v8::Date> FXJS_NewDate(v8::Isolate* pIsolate, double d);
 
 int FXJS_ToInt32(v8::Isolate* pIsolate, v8::Local<v8::Value> pValue);
 bool FXJS_ToBoolean(v8::Isolate* pIsolate, v8::Local<v8::Value> pValue);
 double FXJS_ToNumber(v8::Isolate* pIsolate, v8::Local<v8::Value> pValue);
 v8::Local<v8::Object> FXJS_ToObject(v8::Isolate* pIsolate,
                                     v8::Local<v8::Value> pValue);
 CFX_WideString FXJS_ToString(v8::Isolate* pIsolate,
                              v8::Local<v8::Value> pValue);
 v8::Local<v8::Array> FXJS_ToArray(v8::Isolate* pIsolate,
                                   v8::Local<v8::Value> pValue);
-void FXJS_ValueCopy(v8::Local<v8::Value>& pTo, v8::Local<v8::Value> pFrom);
-
 #endif  // FXJS_INCLUDE_FXJS_V8_H_