libchromeos: Move Dictionary class into its own header file

Moved chromeos::dbus_utils::Dictionary type alias into its
own header file (chromeos/dictionary.h) and promoting it to the
top level namespace (chromeos).

So now it becomes chromeos::VariantDictionary and it is now
independent from D-Bus data serialization.

BUG=None
TEST=FEATURE=test emerge-link libchromeos buffet

Change-Id: Ibad63fd4168d77b9a4b80c7800016510f87ae33d
Reviewed-on: https://chromium-review.googlesource.com/219413
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/libbuffet/command.h b/buffet/libbuffet/command.h
index 3404898..15fbb7b 100644
--- a/buffet/libbuffet/command.h
+++ b/buffet/libbuffet/command.h
@@ -9,8 +9,7 @@
 
 #include <base/macros.h>
 #include <base/memory/weak_ptr.h>
-#include <chromeos/any.h>
-#include <chromeos/dbus/data_serialization.h>
+#include <chromeos/variant_dictionary.h>
 
 #include "libbuffet/export.h"
 
@@ -37,7 +36,7 @@
   // Returns the command category.
   const std::string& GetCategory() const;
   // Returns the command parameters and their values.
-  const chromeos::dbus_utils::Dictionary& GetParameters() const;
+  const chromeos::VariantDictionary& GetParameters() const;
 
   // Updates the command execution progress. The |progress| must be between
   // 0 and 100. Returns false if the progress value is incorrect.