File constructor understands lastModified.

Source/bindings/v8/V8Binding.h

 /*
 * Copyright (C) 2009 Google Inc. All rights reserved.
 * Copyright (C) 2012 Ericsson AB. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
@@ skipping 628 matching lines @@
     // we need to use v8BooleanWithCheck(value, isolate) if an isolate can be null.
     //
     // FIXME: Remove all null isolates from V8 bindings, and remove v8BooleanWithCheck(value, isolate).
     inline v8::Handle<v8::Boolean> v8BooleanWithCheck(bool value, v8::Isolate* isolate)
     {
         return isolate ? v8Boolean(value, isolate) : v8Boolean(value);
     }
 
     inline double toWebCoreDate(v8::Handle<v8::Value> object)
     {
-        return (object->IsDate() || object->IsNumber()) ? object->NumberValue() : std::numeric_limits<double>::quiet_NaN();
+        if (object->IsDate())
+            return v8::Handle<v8::Date>::Cast(object)->ValueOf();
+        if (object->IsNumber())
+            return object->NumberValue();
+        return std::numeric_limits<double>::quiet_NaN();
     }
 
     inline v8::Handle<v8::Value> v8DateOrNull(double value, v8::Isolate* isolate)
     {
         ASSERT(isolate);
         return std::isfinite(value) ? v8::Date::New(value) : v8NullWithCheck(isolate);
     }
 
     v8::Handle<v8::FunctionTemplate> createRawTemplate(v8::Isolate*);
 
@@ skipping 61 matching lines @@
 
     v8::Isolate* mainThreadIsolate();
     v8::Isolate* toIsolate(ExecutionContext*);
     v8::Isolate* toIsolate(Frame*);
 
     // Can only be called by blink::initialize
     void setMainThreadIsolate(v8::Isolate*);
 } // namespace WebCore
 
 #endif // V8Binding_h