components: Introduce AlarmTimer class and use it for GCM heartbeat

components/timers.gypi

Index: components/timers.gypi
diff --git a/components/language_usage_metrics.gypi b/components/timers.gypi
similarity index 65%
copy from components/language_usage_metrics.gypi
copy to components/timers.gypi
index e150a1bba9e6673d38945da908c9edd17bea6fcc..4202b96fc34fca18dba2395029d1d10ea3b2dece 100644
--- a/components/language_usage_metrics.gypi
+++ b/components/timers.gypi
@@ -5,18 +5,21 @@
 {
   'targets': [
     {
-      'target_name': 'language_usage_metrics',
+      # GN version: //components/timers
+      'target_name': 'timers',
       'type': 'static_library',
-      'dependencies': [
-        '../base/base.gyp:base',
-      ],
       'include_dirs': [
         '..',
       ],
+      'dependencies': [
+        '../base/base.gyp:base',
+      ],
       'sources': [
-        'language_usage_metrics/language_usage_metrics.cc',
-        'language_usage_metrics/language_usage_metrics.h',
+        'timers/alarm_timer.cc',
+        'timers/alarm_timer.h',
+        'timers/rtc_alarm.cc',
+        'timers/rtc_alarm.h',
       ],
     },
   ],
-}
+}