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..6c6d874e2dd25452753b87e5801a6886f47a16ee 100644
--- a/ui/events/cocoa/events_mac.mm
+++ b/ui/events/cocoa/events_mac.mm
@@ -12,8 +12,10 @@
 #import "base/mac/sdk_forward_declarations.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
+#include "ui/events/base_event_utils.h"
 #include "ui/events/cocoa/cocoa_event_utils.h"
 #include "ui/events/event_utils.h"
+

[miu, 2016/05/16 20:05:35]

Please remove blank line here.

[majidvp, 2016/05/21 01:38:00]

Done.

 #import "ui/events/keycodes/keyboard_code_conversion_mac.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/vector2d.h"
@@ -77,14 +79,14 @@ 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 ui::EventTimeStampFromSeconds(seconds) +

[miu, 2016/05/16 20:05:35]

This feels brittle. How will you ensure this remains in-line with the
base/time/time_mac.mm implementation? Perhaps you should write a unit test (or
at least some DCHECKing) to ensure this translation is always correct?

[majidvp, 2016/05/21 01:38:00]

Good point. I added a DCHECK to ensure it is within a reasonable distance of
TimeTicks::Now.

Note that we already track this in UMA and it is pretty clear that we should
never hit that DCHECK on Mac OS:
https://uma.googleplex.com/p/chrome/histograms/?endDate=05-18-2016&dayCount=2...
 

Also will look into how I can get Mac OS to generate event for testing purpose
and see if I can write a test for that.

+         base::TimeDelta::FromMicroseconds(microseconds);
 }
 
 gfx::Point EventLocationFromNative(const base::NativeEvent& native_event) {