Add documentation for platform/bindings

third_party/WebKit/Source/platform/bindings/TraceWrapperReference.md

 # Wrapper Tracing Reference
 
 This document describes wrapper tracing and how its API is supposed to be used.
 
 [TOC]
 
 ## Quickstart guide
 
 Wrapper tracing is used to represent reachability across V8 and Blink. The
 following checklist highlights the modifications needed to make a class
 participate in wrapper tracing.
 
 1. Make sure that objects participating in tracing either inherit from
 ``ScriptWrappable`` (if they can reference wrappers) or ``TraceWrapperBase``
 (transitively holding wrappers alive).
 2. Use ``TraceWrapperMember<T>`` to annotate fields that need to be followed to
 find other wrappers that this object should keep alive.
 3. Use ``TraceWrapperV8Reference<T>`` to annotate references to V8 that this
 object should keep alive.
 4. Declare a method to trace other wrappers using
 ``DECLARE_VIRTUAL_TRACE_WRAPPERS()``.
 5. Define the method using ``DEFINE_TRACE_WRAPPERS(ClassName)``.
 6. Trace all fields that received a wrapper tracing type in (1) and (2) using
 ``visitor->traceWrapers(<m_field>)`` in the body of ``DEFINE_TRACE_WRAPPERS``.
 
 The following example illustrates these steps:
 
 ```c++
-#include "bindings/core/v8/ScriptWrappable.h"
-#include "bindings/core/v8/TraceWrapperMember.h"
-#include "bindings/core/v8/TraceWrapperV8Reference.h"
+#include "platform/bindings/ScriptWrappable.h"
+#include "platform/bindings/TraceWrapperMember.h"
+#include "platform/bindings/TraceWrapperV8Reference.h"
 
 class SomeDOMObject : public ScriptWrappable {          // (1)
  public:
   DECLARE_VIRTUAL_TRACE_WRAPPERS();                     // (4)
 
  private:
   TraceWrapperMember<OtherWrappable> m_otherWrappable;  // (2)
   Member<NonWrappable> m_nonWrappable;
   TraceWrapperV8Reference<v8::Value> m_v8object;        // (3)
   // ...
@@ skipping 32 matching lines @@
 
 [object-grouping-slides]: https://docs.google.com/presentation/d/1I6leiRm0ysSTqy7QWh33Gfp7_y4ngygyM2tDAqdF0fI/
 [oilpan-docs]: https://chromium.googlesource.com/chromium/src/+/master/third_party/WebKit/Source/platform/heap/BlinkGCAPIReference.md
 
 ## Basic usage
 
 The annotations that are required can be found in the following header files.
 Pick the header file depending on what types are needed.
 
 ```c++
-#include "bindings/core/v8/ScriptWrappable.h"
-#include "bindings/core/v8/TraceWrapperBase.h"
-#include "bindings/core/v8/TraceWrapperMember.h"
-#include "bindings/core/v8/TraceWrapperV8Reference.h"
+#include "platform/bindings/ScriptWrappable.h"
+#include "platform/bindings/TraceWrapperMember.h"
+#include "platform/bindings/TraceWrapperV8Reference.h"
 ```
 
 The following example will guide through the modifications that are needed to
 adjust a given class ``SomeDOMObject`` to participate in wrapper tracing.
 
 ```c++
 class SomeDOMObject : public ScriptWrappable {
   // ...
  private:
   Member<OtherWrappable /* extending ScriptWrappable */> m_otherWrappable;
@@ skipping 181 matching lines @@
   DECLARE_VIRTUAL_TRACE_WRAPPERS();
  private:
   Member<OtherWrappable>> m_otherWrappable;
 };
 
 DEFINE_TRACE_WRAPPERS(ManualWrappable) {
   for (auto other : m_otherWrappables)
     visitor->traceWrappersWithManualWriteBarrier(other);
 }
 ```