[Cleanup] Use a sequence checker rather than a thread checker for the metrics service.

chrome/browser/metrics/chrome_metrics_service_client.h

Index: chrome/browser/metrics/chrome_metrics_service_client.h
diff --git a/chrome/browser/metrics/chrome_metrics_service_client.h b/chrome/browser/metrics/chrome_metrics_service_client.h
index bfb2ccd1d6f9eb3a9d61e18382e8ae8a0347ae3d..293b6eee1ef36934bc2113b8114b352b18cf72f6 100644
--- a/chrome/browser/metrics/chrome_metrics_service_client.h
+++ b/chrome/browser/metrics/chrome_metrics_service_client.h
@@ -15,7 +15,7 @@
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
-#include "base/threading/thread_checker.h"
+#include "base/sequence_checker.h"
 #include "build/build_config.h"
 #include "chrome/browser/metrics/metrics_memory_details.h"
 #include "components/metrics/metrics_log_uploader.h"
@@ -171,7 +171,7 @@ class ChromeMetricsServiceClient : public metrics::MetricsServiceClient,
   void CountBrowserCrashDumpAttempts();
 #endif  // OS_WIN
 
-  base::ThreadChecker thread_checker_;
+  SEQUENCE_CHECKER(sequence_checker_);
 
   // Weak pointer to the MetricsStateManager.
   metrics::MetricsStateManager* metrics_state_manager_;