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}

tools/gen-postmortem-metadata.py

@@ -150,9 +150,11 @@ extras_accessors = [
     'HeapObject, map, Map, kMapOffset',
     'JSObject, elements, Object, kElementsOffset',
     'FixedArray, data, uintptr_t, kHeaderSize',
+    'JSArrayBuffer, backing_store, Object, kBackingStoreOffset',
+    'JSArrayBufferView, byte_offset, Object, kByteOffsetOffset',
     'JSTypedArray, length, Object, kLengthOffset',
     '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',