Add source column to chrome://policy showing the origins of policies.

components/policy/core/common/async_policy_provider.cc

Index: components/policy/core/common/async_policy_provider.cc
diff --git a/components/policy/core/common/async_policy_provider.cc b/components/policy/core/common/async_policy_provider.cc
index ae08b209efb78d754da5910356821d7513d00c43..9c92b32c09d2b655bd70f3e20e124d7a2d56f17f 100644
--- a/components/policy/core/common/async_policy_provider.cc
+++ b/components/policy/core/common/async_policy_provider.cc
@@ -21,6 +21,8 @@ AsyncPolicyProvider::AsyncPolicyProvider(
     scoped_ptr<AsyncPolicyLoader> loader)
     : loader_(loader.Pass()),
       weak_factory_(this) {
+  // The loaders always read policies from local platform sources.
+  source_ = POLICY_SOURCE_PLATFORM;
   // Make an immediate synchronous load on startup.
   OnLoaderReloaded(loader_->InitialLoad(registry->schema_map()));
 }