diff -r 000000000000 -r 6474c204b198 xpcom/reflect/xptinfo/src/xptiWorkingSet.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/reflect/xptinfo/src/xptiWorkingSet.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,54 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Implementation of xptiWorkingSet. */
+
+#include "mozilla/XPTInterfaceInfoManager.h"
+
+#include "xptiprivate.h"
+#include "nsString.h"
+
+using namespace mozilla;
+
+#define XPTI_STRUCT_ARENA_BLOCK_SIZE    (1024 * 16)
+#define XPTI_HASHTABLE_SIZE             2048
+
+XPTInterfaceInfoManager::xptiWorkingSet::xptiWorkingSet()
+    : mTableReentrantMonitor("xptiWorkingSet::mTableReentrantMonitor")
+    , mIIDTable(XPTI_HASHTABLE_SIZE)
+    , mNameTable(XPTI_HASHTABLE_SIZE)
+{
+    MOZ_COUNT_CTOR(xptiWorkingSet);
+
+    gXPTIStructArena = XPT_NewArena(XPTI_STRUCT_ARENA_BLOCK_SIZE, sizeof(double),
+                                    "xptiWorkingSet structs");
+}        
+
+static PLDHashOperator
+xpti_Invalidator(const char* keyname, xptiInterfaceEntry* entry, void* arg)
+{
+    entry->LockedInvalidateInterfaceInfo();
+    return PL_DHASH_NEXT;
+}
+
+void 
+XPTInterfaceInfoManager::xptiWorkingSet::InvalidateInterfaceInfos()
+{
+    ReentrantMonitorAutoEnter monitor(mTableReentrantMonitor);
+    mNameTable.EnumerateRead(xpti_Invalidator, nullptr);
+}        
+
+XPTInterfaceInfoManager::xptiWorkingSet::~xptiWorkingSet()
+{
+    MOZ_COUNT_DTOR(xptiWorkingSet);
+
+    // Only destroy the arena if we're doing leak stats. Why waste shutdown
+    // time touching pages if we don't have to?
+#ifdef NS_FREE_PERMANENT_DATA
+    XPT_DestroyArena(gXPTIStructArena);
+#endif
+}
+
+XPTArena* gXPTIStructArena;