platform2: Move Error class from Buffet to libchromeos

Moved buffet::Error class and related facilities to
libchromeos and changed the namespace to 'chromeos::'.
Updated a bunch of code to include the header files
from the new location and referring to the new
namespace.

BUG=chromium:403604
TEST=USE=buffet ./build_packages
     FEATURES=test emerge-link libchromeos
     USE=buffet FEATURES=test emerge-link platform2

Change-Id: I0b5b37ccd7ee3b7be9467ebfae5d172d9b057cf6
Reviewed-on: https://chromium-review.googlesource.com/212525
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/commands/command_dictionary_unittest.cc b/buffet/commands/command_dictionary_unittest.cc
index 30d185f..d4c4ab1 100644
--- a/buffet/commands/command_dictionary_unittest.cc
+++ b/buffet/commands/command_dictionary_unittest.cc
@@ -53,7 +53,7 @@
 
 TEST(CommandDictionary, LoadCommands_Failures) {
   buffet::CommandDictionary dict;
-  buffet::ErrorPtr error;
+  chromeos::ErrorPtr error;
 
   // Command definition missing 'parameters' property.
   auto json = CreateDictionaryValue("{'robot':{'jump':{}}}");
@@ -97,7 +97,7 @@
 TEST(CommandDictionary, LoadCommands_RedefineInDifferentCategory) {
   // Redefine commands in different category.
   buffet::CommandDictionary dict;
-  buffet::ErrorPtr error;
+  chromeos::ErrorPtr error;
   auto json = CreateDictionaryValue("{'robot':{'jump':{'parameters':{}}}}");
   dict.LoadCommands(*json, "category1", nullptr, &error);
   EXPECT_FALSE(dict.LoadCommands(*json, "category2", nullptr, &error));
@@ -111,7 +111,7 @@
   // Custom command must start with '_'.
   buffet::CommandDictionary base_dict;
   buffet::CommandDictionary dict;
-  buffet::ErrorPtr error;
+  chromeos::ErrorPtr error;
   auto json = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
@@ -137,7 +137,7 @@
   // Redefine commands parameter type.
   buffet::CommandDictionary base_dict;
   buffet::CommandDictionary dict;
-  buffet::ErrorPtr error;
+  chromeos::ErrorPtr error;
   auto json = CreateDictionaryValue(R"({
     'base': {
       'reboot': {