Use high precision timestamp for Event.timestamp

third_party/WebKit/Source/core/events/Event.cpp

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2005, 2006, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 11 matching lines @@
 
 #include "config.h"
 #include "core/events/Event.h"
 
 #include "core/dom/StaticNodeList.h"
 #include "core/events/EventDispatchMediator.h"
 #include "core/events/EventTarget.h"
 #include "core/frame/OriginsUsingFeatures.h"
 #include "core/frame/UseCounter.h"
 #include "core/svg/SVGElement.h"
+#include "core/timing/PerformanceBase.h"
 #include "wtf/CurrentTime.h"
 
 namespace blink {
 
+static const double millisPerSecond = 1000.0;
+
 Event::Event()
     : Event("", false, false)
 {
 }
 
 Event::Event(const AtomicString& eventType, bool canBubbleArg, bool cancelableArg)
     : m_type(eventType)
     , m_canBubble(canBubbleArg)
     , m_cancelable(cancelableArg)
     , m_propagationStopped(false)
     , m_immediatePropagationStopped(false)
     , m_defaultPrevented(false)
     , m_defaultHandled(false)
     , m_cancelBubble(false)
     , m_isTrusted(false)
     , m_eventPhase(0)
     , m_currentTarget(nullptr)
     , m_createTime(convertSecondsToDOMTimeStamp(currentTime()))
-    , m_uiCreateTime(0)
+    , m_platformTimeStamp(monotonicallyIncreasingTime())
 {
 }
 
 Event::Event(const AtomicString& eventType, const EventInit& initializer)
     : Event(eventType, initializer.bubbles(), initializer.cancelable())
 {
 }
 
 Event::~Event()
 {
@@ skipping 185 matching lines @@
     if (!m_currentTarget)
         return nullptr;
     Node* node = m_currentTarget->toNode();
     if (node && node->isSVGElement()) {
         if (SVGElement* svgElement = toSVGElement(node)->correspondingElement())
             return svgElement;
     }
     return m_currentTarget.get();
 }
 
+double Event::timeStamp(ScriptState* scriptState) const
+{
+    double timeStamp = 0;
+    // TODO(majidvp): Get rid of m_createTime once the flag is enabled by default;
+    if (UNLIKELY(RuntimeEnabledFeatures::hiResEventTimeStampEnabled())) {
+        // Only expose monotonic time after changing its origin to its target
+        // document's time origin.
+        if (scriptState && scriptState->domWindow() && scriptState->domWindow()->document()) {

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

It feels a little weird to depend on a Document here, but I don't immediately
see a way to go direct to the LocalFrame.  I _think_ the special cases like
extensions will be OK but I won't be surprised if we're missing some case
(that'll show up with a timestamp of value 0 or with the wrong time base).  But
since this is still behind a flag, it's fine to land it as-is and then do some
experiments.

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

There is a way to obtain the performance timing directly from window[1]  which
bypasses the document. I switched this to use it.


[1]https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/core/timing/DOMWindowPerformance.h&sq=package:chromium&l=26&q=DOMWindowPerformance::performance

[Rick Byers, 2015/09/29 15:57:59]

Nice, this makes a lot more sense to me (and seems safer too) - thanks!

+            double docTimeStamp = scriptState->domWindow()->document()->monotonicTimeToZeroBasedDocumentTime(m_platformTimeStamp);
+            timeStamp =  toSafePrecisionTime(docTimeStamp) * millisPerSecond;
+        }
+    } else {
+        timeStamp = m_createTime;
+    }
+
+    return timeStamp;
+}
+
 DEFINE_TRACE(Event)
 {
     visitor->trace(m_currentTarget);
     visitor->trace(m_target);
     visitor->trace(m_underlyingEvent);
     visitor->trace(m_eventPath);
 }
 
 } // namespace blink