Move MetricsStateManager into the Metrics component.

chrome/common/pref_names.h

Index: chrome/common/pref_names.h
diff --git a/chrome/common/pref_names.h b/chrome/common/pref_names.h
index 0445e24387093138e8f34c75421070b6fecf38a2..de502621ad56337fb3b5b79cc193dd75d8a37c9c 100644
--- a/chrome/common/pref_names.h
+++ b/chrome/common/pref_names.h
@@ -14,6 +14,7 @@
 #include "components/autofill/core/common/autofill_pref_names.h"
 #include "components/bookmarks/common/bookmark_pref_names.h"
 #include "components/data_reduction_proxy/common/data_reduction_proxy_pref_names.h"
+#include "components/metrics/metrics_pref_names.h"
 #include "components/signin/core/common/signin_pref_names.h"
 
 namespace prefs {
@@ -425,13 +426,8 @@ extern const char kGLVersionString[];
 
 extern const char kEulaAccepted[];
 
-extern const char kMetricsClientID[];
-extern const char kMetricsSessionID[];
-extern const char kMetricsLowEntropySource[];
-extern const char kMetricsOldClientID[];
-extern const char kMetricsOldLowEntropySource[];
 extern const char kMetricsReportingEnabled[];
-extern const char kMetricsReportingEnabledTimestamp[];
+
 // Android has it's own metric / crash reporting implemented in Android
 // Java code so kMetricsReportingEnabled doesn't make sense. We use this
 // to inform crashes_ui that we have enabled crash reporting.