Use high precision timestamp for Event.timestamp

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

Index: third_party/WebKit/Source/core/events/Event.cpp
diff --git a/third_party/WebKit/Source/core/events/Event.cpp b/third_party/WebKit/Source/core/events/Event.cpp
index 05c35a686ddbe70d07317c570f31dbe14db7f3da..59166484843deb86aae9b5d4d75a5e04329c0efb 100644
--- a/third_party/WebKit/Source/core/events/Event.cpp
+++ b/third_party/WebKit/Source/core/events/Event.cpp
@@ -29,10 +29,13 @@
 #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)
 {
@@ -51,7 +54,7 @@ Event::Event(const AtomicString& eventType, bool canBubbleArg, bool cancelableAr
     , m_eventPhase(0)
     , m_currentTarget(nullptr)
     , m_createTime(convertSecondsToDOMTimeStamp(currentTime()))
-    , m_uiCreateTime(0)
+    , m_platformTimeStamp(monotonicallyIncreasingTime())
 {
 }
 
@@ -257,6 +260,24 @@ EventTarget* Event::currentTarget() const
     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);