Add comments to wtf/AtomciString.h.

third_party/WebKit/Source/wtf/text/AtomicString.h

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 16 matching lines @@
 #include "wtf/text/CString.h"
 #include "wtf/text/StringView.h"
 #include "wtf/text/WTFString.h"
 #include <cstring>
 #include <iosfwd>
 
 namespace WTF {
 
 struct AtomicStringHash;
 
+// An AtomicString instance represents a string, and multiple AtomicString
+// instances can shares their string storage if the strings are

[kochi, 2016/12/01 07:16:56]

nit: can share (without s)

[tkent, 2016/12/01 08:24:30]

oops.  Done.

+// identical. Comparing two AtomicString instances is much faster than comparing
+// two String instances because we just check string storage identity.
+//
+// AtomicString instances are not thread-safe. An AtomicString instance created
+// in a thread must be used only in the creator thread.  If multiple threads
+// access a single AtomicString instance, we have race condition of a reference
+// count in StringImpl, and would hit a runtime CHECK in
+// AtomicStringTable::remove().
+//
+// Exception: nullAtom and emptyAtom, are shared in multiple threads, and are
+// never stored in AtomicStringTable.
 class WTF_EXPORT AtomicString {
   USING_FAST_MALLOC(AtomicString);
 
  public:
+  // The function is defined in StringStatics.cpp.
   static void init();
 
   AtomicString() {}
   AtomicString(const LChar* chars)
       : AtomicString(chars,
                      chars ? strlen(reinterpret_cast<const char*>(chars)) : 0) {
   }
   AtomicString(const char* chars)
       : AtomicString(reinterpret_cast<const LChar*>(chars)) {}
   AtomicString(const LChar* chars, unsigned length);
@@ skipping 255 matching lines @@
 using WTF::AtomicString;
 using WTF::nullAtom;
 using WTF::emptyAtom;
 using WTF::starAtom;
 using WTF::xmlAtom;
 using WTF::xmlnsAtom;
 using WTF::xlinkAtom;
 
 #include "wtf/text/StringConcatenate.h"
 #endif  // AtomicString_h