Extensions: Store disable reasons in Sync

sync/protocol/extension_specifics.proto

Index: sync/protocol/extension_specifics.proto
diff --git a/sync/protocol/extension_specifics.proto b/sync/protocol/extension_specifics.proto
index 8e724a31916b367da696b8021c11feab393c0ba8..81becdcb9e0fb6e3dd4d2eee4dcb4ba518bb7ad5 100644
--- a/sync/protocol/extension_specifics.proto
+++ b/sync/protocol/extension_specifics.proto
@@ -48,5 +48,9 @@ message ExtensionSpecifics {
   // optional and may be absent. We need this for the time being because we need
   // to know if a user has not set an explicit preference.
   optional bool all_urls_enabled = 9;
+
+  // Bitmask of the set of reasons why the extension is disabled (see
+  // Extension::DisableReason). Only relevant when enabled == false.

[not at google - send to devlin, 2015/05/12 18:04:17]

You might also want to add that older clients won't set this, even if enabled is
false. I see that you've added logic that deals with that already, but I don't
see it tested.

[Marc Treib, 2015/05/19 12:12:03]

Done.

+  optional int32 disable_reasons = 10;
 }