Bug 671299 (part 2) - Add nsStringBuffer::SizeOfIncludingThisMustBeUnshared. r=bz.

xpcom/string/public/nsStringBuffer.h

@@ -170,6 +170,12 @@ class nsStringBuffer
       void ToString(PRUint32 len, nsACString &str,
                            bool aMoveOwnership = false);
 
+      /**
+       * This measures the size.  It should only be used if the StringBuffer is
+       * unshared.  This is checked.
+       */
+      size_t SizeOfIncludingThisMustBeUnshared(nsMallocSizeOfFun aMallocSizeOf) const;
+
       /**
        * This measures the size only if the StringBuffer is unshared.
        */

xpcom/string/src/nsSubstring.cpp

@@ -307,12 +307,20 @@ nsStringBuffer::ToString(PRUint32 len, nsACString &str,
     accessor->set(data, len, flags);
   }
 
+size_t
+nsStringBuffer::SizeOfIncludingThisMustBeUnshared(nsMallocSizeOfFun aMallocSizeOf) const
+  {
+    NS_ASSERTION(!IsReadonly(),
+                 "shared StringBuffer in SizeOfIncludingThisMustBeUnshared");
+    return aMallocSizeOf(this);
+  }
+
 size_t
 nsStringBuffer::SizeOfIncludingThisIfUnshared(nsMallocSizeOfFun aMallocSizeOf) const
   {
     if (!IsReadonly())
       {
-        return aMallocSizeOf(this);
+        return SizeOfIncludingThisMustBeUnshared(aMallocSizeOf);
       }
     return 0;
   }