Encapsulate element handling into a class keyed on ElementsKind

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index ba690ecab52c1cfafbe4a2e511134fc247a4328d..27082f7799350a1a74f8457a7ee5cde00c952d2e 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -71,17 +71,19 @@
 //         - ExternalIntArray
 //         - ExternalUnsignedIntArray
 //         - ExternalFloatArray
-//       - FixedArray
-//         - DescriptorArray
-//         - HashTable
-//           - Dictionary
-//           - SymbolTable
-//           - CompilationCacheTable
-//           - CodeCacheHashTable
-//           - MapCache
-//         - Context
-//         - JSFunctionResultCache
-//         - SerializedScopeInfo
+//       - FixedArrayBase
+//         - FixedArray
+//           - DescriptorArray
+//           - HashTable
+//             - Dictionary
+//             - SymbolTable
+//             - CompilationCacheTable
+//             - CodeCacheHashTable
+//             - MapCache
+//           - Context
+//           - JSFunctionResultCache
+//           - SerializedScopeInfo
+//         - FixedDoubleArray
 //       - String
 //         - SeqString
 //           - SeqAsciiString
@@ -630,8 +632,10 @@ enum CompareResult {
                          WriteBarrierMode mode = UPDATE_WRITE_BARRIER); \
 
 
+class ElementsAccessor;
 class StringStream;
 class ObjectVisitor;
+class DictionaryElementsAccessor;
 
 struct ValueInfo : public Malloced {
   ValueInfo() : type(FIRST_TYPE), ptr(NULL), str(NULL), number(0) { }
@@ -1488,6 +1492,7 @@ class JSObject: public JSReceiver {
   inline void initialize_elements();
   MUST_USE_RESULT inline MaybeObject* ResetElements();
   inline ElementsKind GetElementsKind();
+  inline ElementsAccessor* GetElementsAccessor();
   inline bool HasFastElements();
   inline bool HasFastDoubleElements();
   inline bool HasDictionaryElements();
@@ -1733,11 +1738,6 @@ class JSObject: public JSReceiver {
   MaybeObject* GetElementWithReceiver(Object* receiver, uint32_t index);
   MaybeObject* GetElementWithInterceptor(Object* receiver, uint32_t index);
 
-  // Get external element value at index if there is one and undefined
-  // otherwise. Can return a failure if allocation of a heap number
-  // failed.
-  MaybeObject* GetExternalElement(uint32_t index);
-
   // Replace the elements' backing store with fast elements of the given
   // capacity.  Update the length for JSArrays.  Returns the new backing
   // store.
@@ -2001,6 +2001,8 @@ class JSObject: public JSReceiver {
   };
 
  private:
+  friend class DictionaryElementsAccessor;
+
   MUST_USE_RESULT MaybeObject* GetElementWithCallback(Object* receiver,
                                                       Object* structure,
                                                       uint32_t index,
@@ -2021,8 +2023,6 @@ class JSObject: public JSReceiver {
       StrictModeFlag strict_mode,
       bool check_prototype);
 
-  MaybeObject* GetElementPostInterceptor(Object* receiver, uint32_t index);
-
   MUST_USE_RESULT MaybeObject* DeletePropertyPostInterceptor(String* name,
                                                              DeleteMode mode);
   MUST_USE_RESULT MaybeObject* DeletePropertyWithInterceptor(String* name);
@@ -2092,6 +2092,7 @@ class FixedArray: public FixedArrayBase {
   inline Object* get(int index);
   // Setter that uses write barrier.
   inline void set(int index, Object* value);
+  inline bool is_the_hole(int index);
 
   // Setter that doesn't need write barrier).
   inline void set(int index, Smi* value);
@@ -2197,7 +2198,8 @@ class FixedDoubleArray: public FixedArrayBase {
   inline void Initialize(NumberDictionary* from);
 
   // Setter and getter for elements.
-  inline double get(int index);
+  inline double get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, double value);
   inline void set_the_hole(int index);
 
@@ -3129,6 +3131,8 @@ class ExternalArray: public HeapObject {
   inline int length();
   inline void set_length(int value);
 
+  inline bool is_the_hole(int index) { return false; }
+
   // [external_pointer]: The pointer to the external memory area backing this
   // external array.
   DECL_ACCESSORS(external_pointer, void)  // Pointer to the data store.
@@ -3164,7 +3168,8 @@ class ExternalPixelArray: public ExternalArray {
   inline uint8_t* external_pixel_pointer();
 
   // Setter and getter.
-  inline uint8_t get(int index);
+  inline uint8_t get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, uint8_t value);
 
   // This accessor applies the correct conversion from Smi, HeapNumber and
@@ -3192,7 +3197,8 @@ class ExternalPixelArray: public ExternalArray {
 class ExternalByteArray: public ExternalArray {
  public:
   // Setter and getter.
-  inline int8_t get(int index);
+  inline int8_t get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, int8_t value);
 
   // This accessor applies the correct conversion from Smi, HeapNumber
@@ -3220,7 +3226,8 @@ class ExternalByteArray: public ExternalArray {
 class ExternalUnsignedByteArray: public ExternalArray {
  public:
   // Setter and getter.
-  inline uint8_t get(int index);
+  inline uint8_t get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, uint8_t value);
 
   // This accessor applies the correct conversion from Smi, HeapNumber
@@ -3248,7 +3255,8 @@ class ExternalUnsignedByteArray: public ExternalArray {
 class ExternalShortArray: public ExternalArray {
  public:
   // Setter and getter.
-  inline int16_t get(int index);
+  inline int16_t get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, int16_t value);
 
   // This accessor applies the correct conversion from Smi, HeapNumber
@@ -3276,7 +3284,8 @@ class ExternalShortArray: public ExternalArray {
 class ExternalUnsignedShortArray: public ExternalArray {
  public:
   // Setter and getter.
-  inline uint16_t get(int index);
+  inline uint16_t get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, uint16_t value);
 
   // This accessor applies the correct conversion from Smi, HeapNumber
@@ -3304,7 +3313,8 @@ class ExternalUnsignedShortArray: public ExternalArray {
 class ExternalIntArray: public ExternalArray {
  public:
   // Setter and getter.
-  inline int32_t get(int index);
+  inline int32_t get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, int32_t value);
 
   // This accessor applies the correct conversion from Smi, HeapNumber
@@ -3332,7 +3342,8 @@ class ExternalIntArray: public ExternalArray {
 class ExternalUnsignedIntArray: public ExternalArray {
  public:
   // Setter and getter.
-  inline uint32_t get(int index);
+  inline uint32_t get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, uint32_t value);
 
   // This accessor applies the correct conversion from Smi, HeapNumber
@@ -3360,7 +3371,8 @@ class ExternalUnsignedIntArray: public ExternalArray {
 class ExternalFloatArray: public ExternalArray {
  public:
   // Setter and getter.
-  inline float get(int index);
+  inline float get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, float value);
 
   // This accessor applies the correct conversion from Smi, HeapNumber
@@ -3388,7 +3400,8 @@ class ExternalFloatArray: public ExternalArray {
 class ExternalDoubleArray: public ExternalArray {
  public:
   // Setter and getter.
-  inline double get(int index);
+  inline double get_scalar(int index);
+  inline MaybeObject* get(int index);
   inline void set(int index, double value);
 
   // This accessor applies the correct conversion from Smi, HeapNumber