[Sync] Enable Compression from Client to Server by experiment

components/sync/protocol/sync.proto

Index: components/sync/protocol/sync.proto
diff --git a/components/sync/protocol/sync.proto b/components/sync/protocol/sync.proto
index f29afb31f34cdff5feee41dc1a52bf45962e6322..bb60605facf803320a6f367de8acfb7b282af49e 100644
--- a/components/sync/protocol/sync.proto
+++ b/components/sync/protocol/sync.proto
@@ -431,6 +431,10 @@ message CommitMessage {
 
   // Set of optional per-client datatype contexts.
   repeated DataTypeContext client_contexts = 5;
+
+  // This field need to be 256 bytes if set. This attempts to mitigate CRIME
+  // attacks when sync communicate from client to server.

[Nicolas Zea, 2016/10/18 20:23:08]

Call out that this is a 256 byte random string.

Also mention that this is explicitly for clients with compression of client to
server data enabled. If no compression is used, this should not be set.

[Gang Wu, 2016/10/19 00:06:14]

Done.

+  optional string padding = 6;
 };
 
 // This message communicates additional per-type information related to