deps: backport 56a0a79 from V8 upstream

Backport 56a0a797f210e04746f2888116365d29a4bb6afc from V8 upstream to
include post-mortem metadata used by mdb_v8 to support V8 4.6.

Original commit message:

  Update post-mortem metadata generation

  mdb_v8, a post-mortem debugger for Node.js, now uses JSArrayBuffer's
  backing_store property and JSArrayBufferView's byte_offset property to
  get access to the content of Buffer instances in node (which are
  Uint8Array instances). This change adds post-mortem metadata for these
  two properties.

  This change also fixes a typo in
  inobject_properties_of_constructor_function_index_offset that was added
  to gen-postmortem-metadata in a previous change. It should be named
  inobject_properties_or_constructor_function_index instead.

  R=bmeurer@chromium.org

  Review URL: https://codereview.chromium.org/1363403003

  Cr-Commit-Position: refs/heads/master@{#30926}

Ref: https://github.com/nodejs/node/pull/3057
PR-URL: https://github.com/nodejs/node/pull/3351
Reviewed-By: indutny - Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>

deps/v8/tools/gen-postmortem-metadata.py

@@ -151,8 +151,10 @@ extras_accessors = [
     'JSObject, elements, Object, kElementsOffset',
     'FixedArray, data, uintptr_t, kHeaderSize',
     'JSTypedArray, length, Object, kLengthOffset',
+    'JSArrayBuffer, backing_store, Object, kBackingStoreOffset',
+    'JSArrayBufferView, byte_offset, Object, kByteOffsetOffset',
     'Map, instance_attributes, int, kInstanceAttributesOffset',
-    'Map, inobject_properties_of_constructor_function_index_offset, int, kInObjectPropertiesOrConstructorFunctionIndexOffset',
+    'Map, inobject_properties_or_constructor_function_index, int, kInObjectPropertiesOrConstructorFunctionIndexOffset',
     'Map, instance_size, int, kInstanceSizeOffset',
     'Map, bit_field, char, kBitFieldOffset',
     'Map, bit_field2, char, kBitField2Offset',