Ensure that performance.memory is updated on first access.

Source/core/timing/MemoryInfo.cpp

 /*
  * Copyright (C) 2010 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 24 matching lines @@
 #include "core/frame/Settings.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/MainThread.h"
 #include "wtf/MathExtras.h"
 #include "wtf/ThreadSpecific.h"
 #include <limits>
 
 namespace blink {
 
+static const double TwentyMinutesInSeconds = 20 * 60;
+
 class HeapSizeCache {
     WTF_MAKE_NONCOPYABLE(HeapSizeCache); WTF_MAKE_FAST_ALLOCATED;
 public:
     HeapSizeCache()
-        : m_lastUpdateTime(0)
+        : m_lastUpdateTime(monotonicallyIncreasingTime() - TwentyMinutesInSeconds)
     {
     }
 
     void getCachedHeapSize(HeapInfo& info)
     {
         maybeUpdate();
         info = m_info;
     }
 
     static HeapSizeCache& forCurrentThread()
     {
         AtomicallyInitializedStaticReference(ThreadSpecific<HeapSizeCache>, heapSizeCache, new ThreadSpecific<HeapSizeCache>);
         return *heapSizeCache;
     }
 
 private:
     void maybeUpdate()
     {
         // We rate-limit queries to once every twenty minutes to make it more difficult
         // for attackers to compare memory usage before and after some event.
-        const double TwentyMinutesInSeconds = 20 * 60;
-
         double now = monotonicallyIncreasingTime();
         if (now - m_lastUpdateTime >= TwentyMinutesInSeconds) {
             update();
             m_lastUpdateTime = now;
         }
     }
 
     void update()
     {
         ScriptGCEvent::getHeapSize(m_info);
@@ skipping 57 matching lines @@
 
 MemoryInfo::MemoryInfo()
 {
     if (RuntimeEnabledFeatures::preciseMemoryInfoEnabled())
         ScriptGCEvent::getHeapSize(m_info);
     else
         HeapSizeCache::forCurrentThread().getCachedHeapSize(m_info);
 }
 
 } // namespace blink