PolicyManager: Mark protected members as private.

The Google C++ style guide requires members to be private having
a getter and setter with fixed names. This patch moves the protected
members to the private section on the base class for each provider
and adds a protected setter to allow the sub-classes to set these
members on Init().

Also, this patch uniforms the variable names prefixing them with
var_.

BUG=None
TEST=Unit tests still passes.

Change-Id: I4cbf7b7031b430991c12a5c7d9729bafaf359095
Reviewed-on: https://chromium-review.googlesource.com/187979
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
diff --git a/policy_manager/real_random_provider.cc b/policy_manager/real_random_provider.cc
index 81674e4..17ab024 100644
--- a/policy_manager/real_random_provider.cc
+++ b/policy_manager/real_random_provider.cc
@@ -67,7 +67,7 @@
   FILE* fp = fopen(kRandomDevice, "r");
   if (!fp)
     return false;
-  seed_.reset(new RandomSeedVariable("random_seed", fp));
+  set_var_seed(new RandomSeedVariable("seed", fp));
   return true;
 }