Validate that ui::Event::time_stamp comes from the same clock as TimeTicks::Now

ui/events/cocoa/events_mac.mm

 // Copyright 2014 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.
 
 #include "ui/events/event_utils.h"
 
 #include <Cocoa/Cocoa.h>
 #include <stdint.h>
 
 #include "base/logging.h"
@@ skipping 66 matching lines @@
   NSUInteger modifiers = [event modifierFlags];
   return EventFlagsFromNSEventWithModifiers(event, modifiers);
 }
 
 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 ui::EventTimeStampFromSeconds(seconds) +
+  base::TimeTicks timestamp = ui::EventTimeStampFromSeconds(seconds) +
          base::TimeDelta::FromMicroseconds(microseconds);
+  ValidateEventTimeClock(&timestamp);
+  return timestamp;
 }
 
 gfx::Point EventLocationFromNative(const base::NativeEvent& native_event) {
   NSWindow* window = [native_event window];
   if (!window) {
     NOTIMPLEMENTED();  // Point will be in screen coordinates.
     return gfx::Point();
   }
   NSPoint location = [native_event locationInWindow];
   NSRect content_rect = [window contentRectForFrameRect:[window frame]];
@@ skipping 160 matching lines @@
   uint16_t return_value;
   [text getCharacters:&return_value];
   return return_value;
 }
 
 bool IsCharFromNative(const base::NativeEvent& native_event) {
   return false;
 }
 
 }  // namespace ui