PM: Pass TimeDelta by value, not by reference.

BUG=None
TEST=Unit tests.

Change-Id: I5713d195ad8794f2d083f6fe3c433eb1abdad2ba
Reviewed-on: https://chromium-review.googlesource.com/192010
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
diff --git a/policy_manager/generic_variables.h b/policy_manager/generic_variables.h
index 2f9b996..505b180 100644
--- a/policy_manager/generic_variables.h
+++ b/policy_manager/generic_variables.h
@@ -39,7 +39,7 @@
   // GetValue() method is called.
   CopyVariable(const std::string& name, VariableMode mode, const T& ref)
       : Variable<T>(name, mode), ref_(ref) {}
-  CopyVariable(const std::string& name, const base::TimeDelta& poll_interval,
+  CopyVariable(const std::string& name, const base::TimeDelta poll_interval,
                const T& ref)
       : Variable<T>(name, poll_interval), ref_(ref) {}