Change ui::Event::time_stamp from TimeDelta to TimeTicks

ui/events/cocoa/events_mac.mm

Index: ui/events/cocoa/events_mac.mm
diff --git a/ui/events/cocoa/events_mac.mm b/ui/events/cocoa/events_mac.mm
index 55edba342f2f0091c27161563da98bed34b0eeba..12379d5da4ff88e6c4ec5a103b888f1a700423b0 100644
--- a/ui/events/cocoa/events_mac.mm
+++ b/ui/events/cocoa/events_mac.mm
@@ -77,14 +77,14 @@ int EventFlagsFromNative(const base::NativeEvent& event) {
   return EventFlagsFromNSEventWithModifiers(event, modifiers);
 }
 
-base::TimeDelta EventTimeFromNative(const base::NativeEvent& native_event) {
+base::TimeTicks EventTimeFromNative(const base::NativeEvent& native_event) {
   NSTimeInterval since_system_startup = [native_event timestamp];
   // Truncate to extract seconds before doing floating point arithmetic.
   int64_t seconds = since_system_startup;
   since_system_startup -= seconds;
   int64_t microseconds = since_system_startup * 1000000;
-  return base::TimeDelta::FromSeconds(seconds) +
-      base::TimeDelta::FromMicroseconds(microseconds);
+  return base::TimeTicks() + base::TimeDelta::FromSeconds(seconds) +
+         base::TimeDelta::FromMicroseconds(microseconds);
 }
 
 gfx::Point EventLocationFromNative(const base::NativeEvent& native_event) {