Introduce a base pointer field in FixedTypedArrayBase and teach GC about it

src/elements-kind.cc

 // Copyright 2012 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.
 
 #include "src/elements-kind.h"
 
 #include "src/api.h"
 #include "src/base/lazy-instance.h"
 #include "src/elements.h"
 #include "src/objects.h"
@@ skipping 36 matching lines @@
     case SLOPPY_ARGUMENTS_ELEMENTS:
       return kPointerSizeLog2;
   }
   UNREACHABLE();
   return 0;
 }
 
 
 int GetDefaultHeaderSizeForElementsKind(ElementsKind elements_kind) {
   STATIC_ASSERT(FixedArray::kHeaderSize == FixedDoubleArray::kHeaderSize);
-  return IsExternalArrayElementsKind(elements_kind)
-      ? 0 : (FixedArray::kHeaderSize - kHeapObjectTag);
+
+  if (IsExternalArrayElementsKind(elements_kind)) {
+    return 0;
+  } else if (IsFixedTypedArrayElementsKind(elements_kind)) {
+    return FixedTypedArrayBase::kDataOffset - kHeapObjectTag;
+  } else {
+    return FixedArray::kHeaderSize - kHeapObjectTag;
+  }
 }
 
 
 const char* ElementsKindToString(ElementsKind kind) {
   ElementsAccessor* accessor = ElementsAccessor::ForKind(kind);
   return accessor->name();
 }
 
 
 struct InitializeFastElementsKindSequence {
@@ skipping 121 matching lines @@
       default:
         return false;
     }
   }
   return false;
 }
 
 
 }  // namespace internal
 }  // namespace v8