Adding PLM UMA for byte usage by load type

chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h b/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h
index dd31e12a5ee7dbb1b744d7abbfd44435f6727e21..e2f825f56ff6ee80ee2eaaf806f23619b7f16a83 100644
--- a/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h
+++ b/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h
@@ -54,6 +54,18 @@ extern const char kHistogramTotalBytes[];
 extern const char kHistogramNetworkBytes[];
 extern const char kHistogramCacheBytes[];
 
+extern const char kHistogramLoadTypeTotalBytesForwardBack[];
+extern const char kHistogramLoadTypeNetworkBytesForwardBack[];
+extern const char kHistogramLoadTypeCacheBytesForwardBack[];
+
+extern const char kHistogramLoadTypeTotalBytesReload[];
+extern const char kHistogramLoadTypeNetworkBytesReload[];
+extern const char kHistogramLoadTypeCacheBytesReload[];
+
+extern const char kHistogramLoadTypeTotalBytesNewNavigation[];
+extern const char kHistogramLoadTypeNetworkBytesNewNavigation[];
+extern const char kHistogramLoadTypeCacheBytesNewNavigation[];
+
 extern const char kHistogramTotalCompletedResources[];
 extern const char kHistogramNetworkCompletedResources[];
 extern const char kHistogramCacheCompletedResources[];