Add 10 minute random fuzz to automatic update check event schedule.

utils.cc

Index: utils.cc
diff --git a/utils.cc b/utils.cc
index cf1c3f5f11fcfe7fa2af0cf0a80c2f20cfa0a6d2..246bfaa74e94ed8abe414fc50ab701b5668913ad 100644
--- a/utils.cc
+++ b/utils.cc
@@ -20,6 +20,7 @@
 
 #include "base/file_path.h"
 #include "base/file_util.h"
+#include "base/rand_util.h"
 #include "base/string_util.h"
 #include "base/logging.h"
 #include "update_engine/file_writer.h"
@@ -457,6 +458,12 @@ int ComparePriorities(ProcessPriority priority_lhs,
   return static_cast<int>(priority_rhs) - static_cast<int>(priority_lhs);
 }
 
+int FuzzInt(int value, unsigned int range) {
+  int min = value - range / 2;
+  int max = value + range - range / 2;
+  return base::RandInt(min, max);
+}
+
 const char* const kStatefulPartition = "/mnt/stateful_partition";
 
 }  // namespace utils