buffet: load standard GCD command definitions in CommandManager

Changed CommandManager to load the base command definitions
and use it as a base schema for loading device-specific commands
and make sure device vendors are not redefining standard commands
in breaking manner.

BUG=chromium:374861
TEST=USE=buffet P2_TEST_FILTER="buffet::*" FEATURES=test emerge-link platform2

Change-Id: I5f2d5500bc90ef918a8a6df1242bdd1fe3b78615
Reviewed-on: https://chromium-review.googlesource.com/209175
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>

buffet/commands/command_dictionary.h

diff --git a/buffet/commands/command_dictionary.h b/buffet/commands/command_dictionary.h
index 11295c9..78f2cee 100644
--- a/buffet/commands/command_dictionary.h
+++ b/buffet/commands/command_dictionary.h
@@ -46,10 +46,14 @@
   // When LoadCommands is called, all previous definitions of commands from the
   // same category are removed, effectively replacing all the commands in the
   // given category.
+  // Optional |base_commands| parameter specifies the definition of standard
+  // GCD commands for parameter schema validation. Can be set to nullptr if
+  // no validation is needed.
   // Returns false on failure and |error| provides additional error information
   // when provided.
   bool LoadCommands(const base::DictionaryValue& json,
-                    const std::string& category, ErrorPtr* error);
+                    const std::string& category,
+                    const CommandDictionary* base_commands, ErrorPtr* error);
   // Returns the number of command definitions in the dictionary.
   size_t GetSize() const { return definitions_.size(); }
   // Checks if the dictionary has no command definitions.