components: Introduce AlarmTimer class and use it for GCM heartbeat

components/timers/BUILD.gn

Index: components/timers/BUILD.gn
diff --git a/components/language_usage_metrics/BUILD.gn b/components/timers/BUILD.gn
similarity index 65%
copy from components/language_usage_metrics/BUILD.gn
copy to components/timers/BUILD.gn
index 88ad430bd5d7fa51b30734c134e38914e8ab72cd..e0ccaaf848c1011e0244b32ed1b29063cd897d45 100644
--- a/components/language_usage_metrics/BUILD.gn
+++ b/components/timers/BUILD.gn
@@ -2,13 +2,15 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("language_usage_metrics") {
+static_library("timers") {
   sources = [
-    "language_usage_metrics.cc",
-    "language_usage_metrics.h",
+    "alarm_timer.cc",
+    "alarm_timer.h",
+    "rtc_alarm.cc",
+    "rtc_alarm.h",
   ]
 
   deps = [
     "//base",
   ]
-}
+}