Add documentation for platform/bindings

third_party/WebKit/Source/platform/bindings/V8PerContextData.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 40 matching lines @@
 
 class V8DOMActivityLogger;
 class V8PerContextData;
 
 enum V8ContextEmbedderDataField {
   kV8ContextPerContextDataIndex = static_cast<int>(
       gin::kPerContextDataStartIndex +  // NOLINT(readability/enum_casing)
       gin::kEmbedderBlink),             // NOLINT(readability/enum_casing)
 };
 
+// Used to hold data that is associated with a single v8::Context object, and
+// has a 1:1 relationship with v8::Context.
 class PLATFORM_EXPORT V8PerContextData final {
   USING_FAST_MALLOC(V8PerContextData);
   WTF_MAKE_NONCOPYABLE(V8PerContextData);
 
  public:
   static std::unique_ptr<V8PerContextData> Create(v8::Local<v8::Context>);
 
   static V8PerContextData* From(v8::Local<v8::Context>);
 
   ~V8PerContextData();
@@ skipping 72 matching lines @@
   // This is owned by a static hash map in V8DOMActivityLogger.
   V8DOMActivityLogger* activity_logger_;
 
   using DataMap = PersistentHeapHashMap<const char*, Member<Data>>;
   DataMap data_map_;
 };
 
 }  // namespace blink
 
 #endif  // V8PerContextData_h