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/http_transport.h b/buffet/http_transport.h
index e26ee77..15b0bd6 100644
--- a/buffet/http_transport.h
+++ b/buffet/http_transport.h
@@ -11,8 +11,7 @@
 #include <vector>
 
 #include <base/basictypes.h>
-
-#include "buffet/error.h"
+#include <chromeos/error.h>
 
 namespace buffet {
 namespace http {
@@ -42,7 +41,7 @@
       const HeaderList& headers,
       const std::string& user_agent,
       const std::string& referer,
-      ErrorPtr* error) = 0;
+      chromeos::ErrorPtr* error) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Transport);