Use high precision timestamp for Event.timestamp

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 5102 matching lines @@
     // FIXME: Remove this timer once we don't need to compute layout to load plugins.
     if (!m_pluginLoadingTimer.isActive())
         m_pluginLoadingTimer.startOneShot(0, FROM_HERE);
 }
 
 void Document::pluginLoadingTimerFired(Timer<Document>*)
 {
     updateLayout();
 }
 
+double Document::monotonicTimeToZeroBasedDocumentTime(double monotonicTime) const
+{
+    if (!loader())
+        return 0;

[Rick Byers, 2015/09/25 17:29:33]

any idea when this would happen in practice?  Just wondering what bugs might
results.  Is there precedent for using invalid timestamps in such situations? 
Ideally we'd be able to ASSERT that this doesn't happen.

[majidvp, 2015/09/29 14:21:31]

I imagine this can happen if for example one creates a document with
document.implementation.createHTMLDocument().

I changed the implementation so that it uses the same fallback logic as
performance::now() in such cases (i.e., time origin = 0). This will ensure we
are always consistent with performance::now() and timestamps remain relatively
valid.

I am not so sure about the correctness of the performance::now() fallback but
logged a separate ticket for that
https://code.google.com/p/chromium/issues/detail?id=536959 

+
+    return loader()->timing().monotonicTimeToZeroBasedDocumentTime(monotonicTime);
+}
+
 ScriptedAnimationController& Document::ensureScriptedAnimationController()
 {
     if (!m_scriptedAnimationController) {
         m_scriptedAnimationController = ScriptedAnimationController::create(this);
         // We need to make sure that we don't start up the animation controller on a background tab, for example.
         if (!page())
             m_scriptedAnimationController->suspend();
     }
     return *m_scriptedAnimationController;
 }
@@ skipping 611 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     Document::WeakDocumentSet& set = Document::liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().string().utf8().data());
 }
 #endif