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

ui/events/base_event_utils.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_EVENTS_BASE_EVENT_UTILS_H_
 #define UI_EVENTS_BASE_EVENT_UTILS_H_
 
 #include <stdint.h>
 
 #include "ui/events/events_base_export.h"
 
+namespace base {
+class TimeTicks;
+}
+
 // Common functions to be used for all platforms.
 namespace ui {
 
 // Generate an unique identifier for events.
 EVENTS_BASE_EXPORT uint32_t GetNextTouchEventId();
 
 // Checks if |flags| contains system key modifiers.
 EVENTS_BASE_EXPORT bool IsSystemKeyModifier(int flags);
 
+// Converts an event timestamp ticks to seconds (floating point representation).
+// WARNING: This should only be used when interfacing with platform code that
+// does not use base::Time* types.
+EVENTS_BASE_EXPORT double EventTimeStampToSeconds(base::TimeTicks time_stamp);
+
+// Converts an event timestamp in seconds to TimeTicks.
+// WARNING: This should only be used when interfacing with platform code that
+// does not use base::Time* types.
+EVENTS_BASE_EXPORT base::TimeTicks EventTimeStampFromSeconds(
+    double time_stamp_seconds);
+
 }  // namespace ui
 
 #endif  // UI_EVENTS_BASE_EVENT_UTILS_H_