Make CreateTimeCompare to be a strict comparison.

[Android sheriff]
std::sort requires a sorter which satisfies the strict weak ordering.
Otherwise some tests in debug mode crash this way:
~~~
[ RUN      ] ScheduledNotificationManagerTest.DeleteNotifications
algorithm:814: _LIBCPP_ASSERT '!__comp_(__l, __r)' failed. Comparator
does not induce a strict weak ordering
[ CRASHED      ]
~~~

TBR=dtrainor@chromium.org,xingliu@chromium.org

Bug: 1075541
Change-Id: Ic160e2c6201e6bd8702f71658613ab3eb7425a90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2166111Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#762841}

chrome/browser/notifications/scheduler/internal/scheduled_notification_manager.cc

@@ -34,7 +34,7 @@ namespace {
 bool CreateTimeCompare(const NotificationEntry* lhs,
                        const NotificationEntry* rhs) {
   DCHECK(lhs && rhs);
-  return lhs->create_time <= rhs->create_time;
+  return lhs->create_time < rhs->create_time;
 }
 
 // Vailidates notification entry. Returns false if the entry should be deleted.