[Blink] Check thread access in UserGestureIndicator

third_party/WebKit/Source/platform/UserGestureIndicator.cpp

 /*
  * Copyright (C) 2010 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 100 matching lines @@
   int sample = 0;
   if (oldToken.hasGestures())
     sample |= OldTokenHasGesture;
   if (newToken.hasGestures())
     sample |= NewTokenHasGesture;
   gestureMergeHistogram.count(sample);
 }
 
 UserGestureToken* UserGestureIndicator::s_rootToken = nullptr;
 
-UserGestureIndicator::UserGestureIndicator(PassRefPtr<UserGestureToken> token)
-    : m_token(token == s_rootToken ? nullptr : token.get()) {
-  // Silently ignore UserGestureIndicators on non-main threads.
-  if (!isMainThread() || !m_token)
+UserGestureIndicator::UserGestureIndicator(PassRefPtr<UserGestureToken> token) {
+  // Silently ignore UserGestureIndicators on non-main threads and tokens that
+  // are already active.
+  if (!isMainThread() || !token || token == s_rootToken)
     return;
 
+  m_token = token;
   if (!s_rootToken) {
     s_rootToken = m_token.get();
   } else {
     RecordUserGestureMerge(*s_rootToken, *m_token);
     m_token->transferGestureTo(s_rootToken);
   }
   m_token->resetTimestamp();
 }
 
 UserGestureIndicator::~UserGestureIndicator() {
@@ skipping 34 matching lines @@
 }
 
 // static
 UserGestureToken* UserGestureIndicator::currentToken() {
   if (!isMainThread() || !s_rootToken)
     return nullptr;
   return s_rootToken;
 }
 
 }  // namespace blink