Take 2 at browser_sync::ExtensionsActivityMonitor....

chrome/browser/sync/protocol/sync.proto

Index: chrome/browser/sync/protocol/sync.proto
===================================================================
--- chrome/browser/sync/protocol/sync.proto	(revision 30303)
+++ chrome/browser/sync/protocol/sync.proto	(working copy)
@@ -172,6 +172,22 @@
   // A GUID that identifies the committing sync client.  This value will be
   // returned as originator_cache_guid for any new items.
   optional string cache_guid = 2;
+
+  // This message contains diagnostic information used to correlate
+  // commit-related traffic with extensions-related mutations to the
+  // data models in chromium.  It plays no functional role in
+  // processing this CommitMessage.
+  message ChromiumExtensionsActivity {
+    // The human-readable ID identifying the extension responsible
+    // for the traffic reported in this ChromiumExtensionsActivity.
+    optional string extension_id = 1;
+    
+    // How many times the extension successfully invoked a write
+    // operation through the bookmarks API since the last CommitMessage.
+    optional uint32 bookmark_writes_since_last_commit = 2;
+  }
+
+  repeated ChromiumExtensionsActivity extensions_activity = 3;
 };
 
 message GetUpdatesCallerInfo {
@@ -203,7 +219,7 @@
 
 message ClientToServerMessage {
   required string share = 1;
-  optional int32 protocol_version = 2 [default = 21];
+  optional int32 protocol_version = 2 [default = 22];
   enum CONTENTS {
     COMMIT = 1;
     GET_UPDATES = 2;
@@ -243,8 +259,7 @@
     optional string parent_id_string = 4;
 
     // This value is the same as the position_in_parent value returned within
-    // the SyncEntity message in GetUpdatesResponse.  It is returned if the
-    // item was assigned a new position.
+    // the SyncEntity message in GetUpdatesResponse.
     optional int64 position_in_parent = 5;
 
     // The item's current version.