Cleanup usage of kNumNanosecsPerSec like constants in event.cc

Instead rely on TimeDelta constexpr functions to do conversion between
different units of time.

Bug: webrtc:42223979
Change-Id: I7476a2e344303b907a9e297d42bb8fb396fd3aaa
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/401680
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#45202}

rtc_base/BUILD.gn

diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index fc3180f..fdf70e2 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -421,7 +421,6 @@
     ]
     deps = [
       ":checks",
-      ":timeutils",
       "../api/units:time_delta",
       "synchronization:yield_policy",
       "system:warn_current_thread_is_deadlocked",

rtc_base/event.cc

diff --git a/rtc_base/event.cc b/rtc_base/event.cc
index 05f477c..560b036 100644
--- a/rtc_base/event.cc
+++ b/rtc_base/event.cc
@@ -12,14 +12,13 @@
 
 #include <time.h>
 
-#include <cstdint>
+#include <cstdlib>
 #include <optional>
 
 #include "api/units/time_delta.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/synchronization/yield_policy.h"
 #include "rtc_base/system/warn_current_thread_is_deadlocked.h"
-#include "rtc_base/time_utils.h"
 
 #if defined(WEBRTC_WIN)
 #include <windows.h>
@@ -119,7 +118,7 @@
 
 namespace {
 
-timespec GetTimespec(TimeDelta duration_from_now) {
+timespec GetTimespec(TimeDelta from_now) {
   timespec ts;
 
   // Get the current time.
@@ -129,20 +128,15 @@
   timeval tv;
   gettimeofday(&tv, nullptr);
   ts.tv_sec = tv.tv_sec;
-  ts.tv_nsec = tv.tv_usec * kNumNanosecsPerMicrosec;
+  ts.tv_nsec = TimeDelta::Micros(tv.tv_usec).ns();
 #endif
 
-  // Add the specified number of milliseconds to it.
-  int64_t microsecs_from_now = duration_from_now.us();
-  ts.tv_sec += microsecs_from_now / kNumMicrosecsPerSec;
-  ts.tv_nsec +=
-      (microsecs_from_now % kNumMicrosecsPerSec) * kNumNanosecsPerMicrosec;
-
-  // Normalize.
-  if (ts.tv_nsec >= kNumNanosecsPerSec) {
-    ts.tv_sec++;
-    ts.tv_nsec -= kNumNanosecsPerSec;
-  }
+  // Add the specified number of nanoseconds to it.
+  // Use integer division to transfer full seconds to `tv_sec`.
+  // `ns` has type either std::ldiv_t or std::lldiv_t.
+  auto ns = std::div(ts.tv_nsec + from_now.ns(), TimeDelta::Seconds(1).ns());
+  ts.tv_sec += ns.quot;
+  ts.tv_nsec = ns.rem;
 
   return ts;
 }