[Sync] Add histograms for cookie jar state on Sessions commit

sync/sessions/sync_session_context.h

Index: sync/sessions/sync_session_context.h
diff --git a/sync/sessions/sync_session_context.h b/sync/sessions/sync_session_context.h
index 5c61832d41072df5e45840d9c7d5a1db3d3e6231..74213fabf29f1fe66cf2c0af4aafbd938bfdb003 100644
--- a/sync/sessions/sync_session_context.h
+++ b/sync/sessions/sync_session_context.h
@@ -134,6 +134,10 @@ class SYNC_EXPORT SyncSessionContext {
     cookie_jar_mismatch_ = cookie_jar_mismatch;
   }
 
+  bool cookie_jar_empty() const { return cookie_jar_empty_; }
+
+  void set_cookie_jar_empty(bool empty_jar) { cookie_jar_empty_ = empty_jar; }
+
  private:
   // Rather than force clients to set and null-out various context members, we
   // extend our encapsulation boundary to scoped helpers that take care of this
@@ -193,6 +197,9 @@ class SYNC_EXPORT SyncSessionContext {
    // mismatch implies all of them are different from the chrome account.
   bool cookie_jar_mismatch_;
 
+  // If there's a cookie jar mismatch, whether the cookie jar was empty or not.
+  bool cookie_jar_empty_;
+
   DISALLOW_COPY_AND_ASSIGN(SyncSessionContext);
 };