blink: Remove last (non-bindings-tests) occurences of m_instVars.

third_party/WebKit/Source/bindings/core/v8/V8BindingDesign.md

 # Design of V8 bindings
 
 This document explains key concepts in the V8 binding architecture
 except the lifetime management of DOM wrappers.
 See [V8GCController.md](V8GCController.md) to learn the lifetime management.
 
 [TOC]
 
 ## Isolate
 
@@ skipping 207 matching lines @@
 
 To accomplish the semantics that the same DOM wrapper is returned to JavaScript
 as long as the underlying C++ DOM object is alive, we need a mapping
 from the C++ DOM objects to the DOM wrappers.
 In addition, we need to sandbox DOM wrappers in each world.
 To meet the requirements, we make each world hold a DOM wrapper storage
 that stores a mapping from the C++ DOM objects to the DOM wrappers in that world.
 
 As a result, we have multiple DOM wrapper storages in one isolate.
 The mapping of the main world is written in `ScriptWrappable`.
-If `ScriptWrappable::m_mainWorldWrapper` has a non-empty value, it is a DOM
+If `ScriptWrappable::main_world_wrapper_` has a non-empty value, it is a DOM
 wrapper of the C++ DOM object of the main world.
 The mapping of other worlds are written in `DOMWrapperMap`.
 
 ## DOM wrappers and contexts
 
 When you create a new DOM wrapper, you need to choose a correct context
 on which the DOM wrapper is created. If you create a new DOM wrapper in a
 wrong context, you will end up with leaking JavaScript objects to other
 contexts, which is very likely to cause security issues.
 
@@ skipping 17 matching lines @@
 // iframe.html
 <script>
 </script>
 ```
 
 To make sure that a DOM wrapper is created in a correct context, you need to
 make sure that the current context must be set to the correct context
 whenever you call ToV8(). If you're not sure what context to use,
 ask haraken@chromium.org.