Use default timezone on Chromecast linux.

ICU can't detect the system timezone on Chromecast's linux platform, so
we want to use the behavior used on CrOS of pushing the ICU's default
timezone (set by Cast already) to clients.

Bug: internal b/112498903
Test: repro
Change-Id: Idf39a01964d0a5813df3626b0bc33663b7ca3ea3
Reviewed-on: https://chromium-review.googlesource.com/1191123Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Thoren Paulson <thoren@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586411}

services/device/time_zone_monitor/BUILD.gn

@@ -51,6 +51,10 @@ source_set("time_zone_monitor") {
   if (is_fuchsia) {
     sources += [ "time_zone_monitor_fuchsia.cc" ]
   }
+
+  if (is_chromecast) {
+    defines = [ "IS_CHROMECAST" ]
+  }
 }
 
 if (is_android) {

services/device/time_zone_monitor/time_zone_monitor.cc

@@ -29,8 +29,8 @@ void TimeZoneMonitor::Bind(device::mojom::TimeZoneMonitorRequest request) {
 
 void TimeZoneMonitor::NotifyClients() {
   DCHECK(thread_checker_.CalledOnValidThread());
-#if defined(OS_CHROMEOS)
-  // On CrOS, ICU's default tz is already set to a new zone. No
+#if defined(OS_CHROMEOS) || (defined(OS_LINUX) && defined(IS_CHROMECAST))
+  // On CrOS (and Chromecast), ICU's default tz is already set to a new zone. No
   // need to redetect it with detectHostTimeZone().
   std::unique_ptr<icu::TimeZone> new_zone(icu::TimeZone::createDefault());
 #else
@@ -41,7 +41,7 @@ void TimeZoneMonitor::NotifyClients() {
 #else
   std::unique_ptr<icu::TimeZone> new_zone(icu::TimeZone::detectHostTimeZone());
 #endif
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) && !defined(IS_CHROMECAST)
   // We get here multiple times on Linux per a single tz change, but
   // want to update the ICU default zone and notify renderer only once.
   std::unique_ptr<icu::TimeZone> current_zone(icu::TimeZone::createDefault());