PM: Policy for checking whether an update may use the current connection.

This is based on logic currently found in
ConnectionManager::IsUpdateAllowedOver() and
LibcurlHttpFetcher::IsUpdateAllowedOverCurrentConnection().

BUG=chromium:358323
TEST=Unit tests.

Change-Id: Ib1a73d3fbe603b8686294088e26bc2d04ee73877
Reviewed-on: https://chromium-review.googlesource.com/199540
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/updater_provider.h b/policy_manager/updater_provider.h
index ff76cce..293dcdc 100644
--- a/policy_manager/updater_provider.h
+++ b/policy_manager/updater_provider.h
@@ -69,10 +69,11 @@
   // A variable returning the update target channel.
   virtual Variable<std::string>* var_new_channel() = 0;
 
-  // A variable indicating whether P2P updates are allowed.
+  // A variable indicating whether user settings allow P2P updates.
   virtual Variable<bool>* var_p2p_enabled() = 0;
 
-  // A variable indicating whether updates are allowed over a cellular network.
+  // A variable indicating whether user settings allow updates over a cellular
+  // network.
   virtual Variable<bool>* var_cellular_enabled() = 0;
 
   // A variable returning the number of consecutive failed update checks.