[Sync] Refactoring of sync integration test checkers to remove boilerplate await methods.

chrome/browser/sync/test/integration/migration_waiter.h

Index: chrome/browser/sync/test/integration/migration_waiter.h
diff --git a/chrome/browser/sync/test/integration/migration_waiter.h b/chrome/browser/sync/test/integration/migration_waiter.h
index 026bbb578f751ea037ef250f81ed292c51485da9..7e182700b3e713d236caaaaa63559d3bf1e817fe 100644
--- a/chrome/browser/sync/test/integration/migration_waiter.h
+++ b/chrome/browser/sync/test/integration/migration_waiter.h
@@ -5,6 +5,8 @@
 #ifndef CHROME_BROWSER_SYNC_TEST_INTEGRATION_MIGRATION_WAITER_H_
 #define CHROME_BROWSER_SYNC_TEST_INTEGRATION_MIGRATION_WAITER_H_
 
+#include <string>
+
 #include "base/macros.h"
 #include "chrome/browser/sync/test/integration/status_change_checker.h"
 #include "components/sync/base/model_type.h"
@@ -24,13 +26,10 @@ class MigrationWaiter : public StatusChangeChecker {
 
   ~MigrationWaiter() override;
 
-  // Implementation of StatusChangeChecker.
+  // StatusChangeChecker implementation .
   bool IsExitConditionSatisfied() override;
   std::string GetDebugMessage() const override;
 
-  // Function to trigger the waiting.
-  void Wait();
-
   // Callback invoked by our associated waiter when migration state changes.
   void OnMigrationStateChange();