[runtime] Introduce maps for the likely cases of FromPropertyDescriptor.

src/property-descriptor.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_PROPERTY_DESCRIPTOR_H_
 #define V8_PROPERTY_DESCRIPTOR_H_
 
 
 #include "src/handles.h"
 #include "src/property-details.h"
@@ skipping 39 matching lines @@
 
   // ES6 6.2.4.6
   static void CompletePropertyDescriptor(Isolate* isolate,
                                          PropertyDescriptor* desc);
 
   bool is_empty() const {
     return !has_enumerable() && !has_configurable() && !has_writable() &&
            !has_value() && !has_get() && !has_set();
   }
 
+  bool IsRegularAccessorProperty() const {
+    return has_configurable() && has_enumerable() && !has_value() &&
+           !has_writable() && has_get() && has_set();
+  }
+
+  bool IsRegularDataProperty() const {
+    return has_configurable() && has_enumerable() && has_value() &&
+           has_writable() && !has_get() && !has_set();
+  }
+
   bool enumerable() const { return enumerable_; }
   void set_enumerable(bool enumerable) {
     enumerable_ = enumerable;
     has_enumerable_ = true;
   }
   bool has_enumerable() const { return has_enumerable_; }
 
   bool configurable() const { return configurable_; }
   void set_configurable(bool configurable) {
     configurable_ = configurable;
@@ skipping 44 matching lines @@
 
   // Some compilers (Xcode 5.1, ARM GCC 4.9) insist on having a copy
   // constructor for std::vector<PropertyDescriptor>, so we can't
   // DISALLOW_COPY_AND_ASSIGN(PropertyDescriptor); here.
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PROPERTY_DESCRIPTOR_H_