Added a timezone policy and pyauto tests for it.

chrome/browser/policy/proto/chrome_device_policy.proto

Index: chrome/browser/policy/proto/chrome_device_policy.proto
diff --git a/chrome/browser/policy/proto/chrome_device_policy.proto b/chrome/browser/policy/proto/chrome_device_policy.proto
index 5313c88cb5db0848fd9544340e7f8971640f4114..10ab32bd4dd33fef0acdd54ff8994955cb3ac8e0 100644
--- a/chrome/browser/policy/proto/chrome_device_policy.proto
+++ b/chrome/browser/policy/proto/chrome_device_policy.proto
@@ -206,6 +206,11 @@ message StartUpUrlsProto {
   repeated string start_up_urls = 1;
 }
 
+message SystemTimezoneProto {
+  // Specifies the timezone which is applied if this value is provided. 
+  optional string timezone = 1;
+}
+
 message ChromeDeviceSettingsProto {
   optional DevicePolicyRefreshRateProto device_policy_refresh_rate = 1;
   optional UserWhitelistProto user_whitelist = 2;
@@ -226,4 +231,5 @@ message ChromeDeviceSettingsProto {
   optional AutoUpdateSettingsProto auto_update_settings = 17;
   optional StartUpUrlsProto start_up_urls = 18;
   optional PinnedAppsProto pinned_apps = 19;
+  optional SystemTimezoneProto system_timezone = 20;
 }