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

Schedules the initial check at 7 minutes and periodic checks at 45 minutes
with +/- 5 minute fuzz.

BUG=5983
TEST=unit tests, gmerged on device, inspected logs, observed checks

Change-Id: Ifd38574c4265fec78f6e330f965c2b1054b2dddb

Review URL: http://codereview.chromium.org/3173041
diff --git a/utils.h b/utils.h
index 8438313..8b070ed 100644
--- a/utils.h
+++ b/utils.h
@@ -125,6 +125,10 @@
 // Initiates a system reboot. Returns true on success, false otherwise.
 bool Reboot();
 
+// Fuzzes an integer |value| randomly in the range:
+// [value - range / 2, value + range - range / 2]
+int FuzzInt(int value, unsigned int range);
+
 // Log a string in hex to LOG(INFO). Useful for debugging.
 void HexDumpArray(const unsigned char* const arr, const size_t length);
 inline void HexDumpString(const std::string& str) {