PolicyManager: Move payload_size to int64_t.

Code style encourages signed types instead of unsigned types and the
value being exposed is already signed. This patch fixes that for the
payload_size variable and adapts the BoxedValue::ValuePrinter
implementations to use the int64_t and uint64_t types.

BUG=None
TEST=Unit tests updated

Change-Id: I21310c59d8c2654c43cac27265055c8577341562
Reviewed-on: https://chromium-review.googlesource.com/198269
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
diff --git a/policy_manager/real_updater_provider.h b/policy_manager/real_updater_provider.h
index 22b9e0f..7ed0b4e 100644
--- a/policy_manager/real_updater_provider.h
+++ b/policy_manager/real_updater_provider.h
@@ -51,7 +51,7 @@
     return var_new_version_.get();
   }
 
-  virtual Variable<size_t>* var_payload_size() override {
+  virtual Variable<int64_t>* var_payload_size() override {
     return var_payload_size_.get();
   }
 
@@ -87,7 +87,7 @@
   scoped_ptr<Variable<double>> var_progress_;
   scoped_ptr<Variable<Stage>> var_stage_;
   scoped_ptr<Variable<std::string>> var_new_version_;
-  scoped_ptr<Variable<size_t>> var_payload_size_;
+  scoped_ptr<Variable<int64_t>> var_payload_size_;
   scoped_ptr<Variable<std::string>> var_curr_channel_;
   scoped_ptr<Variable<std::string>> var_new_channel_;
   scoped_ptr<Variable<bool>> var_p2p_enabled_;