buffet: Wrap buffet unit tests into buffet namespace

Just to make referencing shorter by removing buffet:: prefix.

BUG=None
TEST=FEATURE=test emerge-gizmo buffet

Change-Id: Ie2cb5645911481c2eb92f80f4847b0faaaea532d
Reviewed-on: https://chromium-review.googlesource.com/268787
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
diff --git a/buffet/states/state_manager_unittest.cc b/buffet/states/state_manager_unittest.cc
index b035175..12d3845 100644
--- a/buffet/states/state_manager_unittest.cc
+++ b/buffet/states/state_manager_unittest.cc
@@ -16,13 +16,13 @@
 #include "buffet/states/error_codes.h"
 #include "buffet/states/mock_state_change_queue_interface.h"
 
-using buffet::unittests::CreateDictionaryValue;
-using buffet::unittests::ValueToString;
-using testing::Return;
-using testing::_;
-
 namespace buffet {
 
+using testing::_;
+using testing::Return;
+using unittests::CreateDictionaryValue;
+using unittests::ValueToString;
+
 namespace {
 std::unique_ptr<base::DictionaryValue> GetTestSchema() {
   return CreateDictionaryValue(R"({