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..2ae0e035849b1852daf253e021d78828283cf497 100644
--- a/third_party/WebKit/Source/core/events/Event.cpp
+++ b/third_party/WebKit/Source/core/events/Event.cpp
@@ -29,6 +29,8 @@
 #include "core/frame/OriginsUsingFeatures.h"
 #include "core/frame/UseCounter.h"
 #include "core/svg/SVGElement.h"
+#include "core/timing/DOMWindowPerformance.h"
+#include "core/timing/Performance.h"
 #include "wtf/CurrentTime.h"
 
 namespace blink {
@@ -51,7 +53,7 @@ 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 +259,24 @@ 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()) {
+            Performance* performance = DOMWindowPerformance::performance(*scriptState->domWindow());
+            timeStamp = performance->monotonicTimeToDOMHighResTimeStamp(m_platformTimeStamp);
+        }
+    } else {
+        timeStamp = m_createTime;
+    }
+
+    return timeStamp;
+}
+
 DEFINE_TRACE(Event)
 {
     visitor->trace(m_currentTarget);