[Sync] Enable Compression from Client to Server by experiment

components/sync/engine_impl/commit.cc

Index: components/sync/engine_impl/commit.cc
diff --git a/components/sync/engine_impl/commit.cc b/components/sync/engine_impl/commit.cc
index abb8fc1b1c063969d0a9e732e098024b0bd4dc78..7c184326fa39e3ec005a34bbba0ea8e94c714120 100644
--- a/components/sync/engine_impl/commit.cc
+++ b/components/sync/engine_impl/commit.cc
@@ -7,10 +7,12 @@
 #include <utility>
 
 #include "base/metrics/sparse_histogram.h"
+#include "base/rand_util.h"
 #include "base/trace_event/trace_event.h"
 #include "components/sync/base/data_type_histogram.h"
 #include "components/sync/engine/events/commit_request_event.h"
 #include "components/sync/engine/events/commit_response_event.h"
+#include "components/sync/engine/net/http_bridge.h"
 #include "components/sync/engine_impl/commit_processor.h"
 #include "components/sync/engine_impl/commit_util.h"
 #include "components/sync/engine_impl/cycle/sync_cycle.h"
@@ -56,6 +58,9 @@ Commit* Commit::Init(ModelTypeSet requested_types,
 
   sync_pb::CommitMessage* commit_message = message.mutable_commit();
   commit_message->set_cache_guid(cache_guid);
+  if (base::FeatureList::IsEnabled(syncer::kSyncClientToServerCompression)) {
+    commit_message->set_padding(base::RandBytesAsString(256));

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

prefer having the length defined at the top of file as a const size_t. As part
of that definition, comment why 256 was chosen.

[Gang Wu, 2016/10/19 00:06:13]

Done.

+  }
 
   // Set extensions activity if bookmark commits are present.
   ExtensionsActivity::Records extensions_activity_buffer;