Reland "LayoutDescriptor should inherit from JSTypedArray"

src/layout-descriptor.h

Index: src/layout-descriptor.h
diff --git a/src/layout-descriptor.h b/src/layout-descriptor.h
index 0a14f53198f5c4fd48dd78b28d4b33d5d8792526..bec442c93597b232fc6fb471996504c3e7864be0 100644
--- a/src/layout-descriptor.h
+++ b/src/layout-descriptor.h
@@ -22,7 +22,7 @@ namespace internal {
 // of the descriptor then the field is also considered tagged.
 // Once a layout descriptor is created it is allowed only to append properties
 // to it.
-class LayoutDescriptor : public FixedTypedArray<Uint32ArrayTraits> {
+class LayoutDescriptor : public JSTypedArray {
  public:
   V8_INLINE bool IsTagged(int field_index);
 
@@ -89,12 +89,17 @@ class LayoutDescriptor : public FixedTypedArray<Uint32ArrayTraits> {
   // Capacity of layout descriptors in bits.
   V8_INLINE int capacity();
 
+  V8_INLINE uint32_t get_scalar(int index);
+  V8_INLINE void set(int index, uint32_t value);
+
   static Handle<LayoutDescriptor> NewForTesting(Isolate* isolate, int length);
   LayoutDescriptor* SetTaggedForTesting(int field_index, bool tagged);
 
  private:
   static const int kNumberOfBits = 32;
 
+  V8_INLINE FixedTypedArray<Uint32ArrayTraits>* GcSafeElements();
+
   V8_INLINE static Handle<LayoutDescriptor> New(Isolate* isolate, int length);
   V8_INLINE static LayoutDescriptor* FromSmi(Smi* smi);