iwyu: Include stringprintf.h where appropriate, part 3.

chrome/test/sync/engine/mock_connection_manager.cc

Index: chrome/test/sync/engine/mock_connection_manager.cc
diff --git a/chrome/test/sync/engine/mock_connection_manager.cc b/chrome/test/sync/engine/mock_connection_manager.cc
index 76c13f147e20edc98d5dad994a3eb3f814e200bb..124027080de4280475045ee2b16abf1aa3c825f7 100644
--- a/chrome/test/sync/engine/mock_connection_manager.cc
+++ b/chrome/test/sync/engine/mock_connection_manager.cc
@@ -8,6 +8,7 @@
 
 #include <map>
 
+#include "base/stringprintf.h"
 #include "chrome/browser/sync/engine/syncer_proto_util.h"
 #include "chrome/browser/sync/protocol/bookmark_specifics.pb.h"
 #include "chrome/test/sync/engine/test_id_factory.h"
@@ -508,7 +509,7 @@ void MockConnectionManager::ProcessCommit(ClientToServerMessage* csm,
     if (entry.has_version() && 0 != entry.version()) {
       er->set_id_string(id);  // Allows verification.
     } else {
-      string new_id = StringPrintf("mock_server:%d", next_new_id_++);
+      string new_id = base::StringPrintf("mock_server:%d", next_new_id_++);
       changed_ids[id] = new_id;
       er->set_id_string(new_id);
     }