Enable ThreadRestrictionVerifier for StringImpl

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

Index: third_party/WebKit/Source/wtf/text/StringImpl.h
diff --git a/third_party/WebKit/Source/wtf/text/StringImpl.h b/third_party/WebKit/Source/wtf/text/StringImpl.h
index 6288b563810dad392f1dfec34c1316107237f0a1..c25ddf1c3b77800c90727714625d8a87fe934c80 100644
--- a/third_party/WebKit/Source/wtf/text/StringImpl.h
+++ b/third_party/WebKit/Source/wtf/text/StringImpl.h
@@ -35,6 +35,10 @@
 #include <limits.h>
 #include <string.h>
 
+#if DCHECK_IS_ON()
+#include "wtf/ThreadRestrictionVerifier.h"
+#endif
+
 #if OS(MACOSX)
 typedef const struct __CFString* CFStringRef;
 #endif
@@ -297,11 +301,25 @@ class WTF_EXPORT StringImpl {
     return hashSlowCase();
   }
 
-  ALWAYS_INLINE bool hasOneRef() const { return m_refCount == 1; }
+  ALWAYS_INLINE bool hasOneRef() const {
+#if DCHECK_IS_ON()
+    DCHECK(isStatic() || m_verifier.isSafeToUse()) << asciiForDebugging();
+#endif
+    return m_refCount == 1;
+  }
 
-  ALWAYS_INLINE void ref() { ++m_refCount; }
+  ALWAYS_INLINE void ref() {
+#if DCHECK_IS_ON()
+    DCHECK(isStatic() || m_verifier.onRef(m_refCount)) << asciiForDebugging();
+#endif
+    ++m_refCount;
+  }
 
   ALWAYS_INLINE void deref() {
+#if DCHECK_IS_ON()
+    DCHECK(isStatic() || m_verifier.onDeref(m_refCount))
+        << asciiForDebugging() << " " << currentThread();
+#endif
     if (!--m_refCount)
       destroyIfNotStatic();
   }
@@ -490,6 +508,10 @@ class WTF_EXPORT StringImpl {
   void destroyIfNotStatic();
   void updateContainsOnlyASCII() const;
 
+#if DCHECK_IS_ON()
+  std::string asciiForDebugging() const;
+#endif
+
 #ifdef STRING_STATS
   static StringStats m_stringStats;
 #endif
@@ -513,6 +535,10 @@ class WTF_EXPORT StringImpl {
   unsigned m_isAtomic : 1;
   const unsigned m_is8Bit : 1;
   const unsigned m_isStatic : 1;
+
+#if DCHECK_IS_ON()
+  mutable ThreadRestrictionVerifier m_verifier;
+#endif
 };
 
 template <>