Add support for single sample metrics.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 7a77da1d6d5ea74edee558d5afb9a60958644a90..0e23262f77232612f391730667dab65b36187d2f 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -51,6 +51,8 @@
 #include "cc/trees/layer_tree_host_common.h"
 #include "cc/trees/layer_tree_settings.h"
 #include "components/discardable_memory/client/client_discardable_shared_memory_manager.h"
+#include "components/metrics/public/interfaces/single_value_histograms.mojom.h"
+#include "components/metrics/single_value_histograms_factory_impl.h"
 #include "content/child/appcache/appcache_dispatcher.h"
 #include "content/child/appcache/appcache_frontend_impl.h"
 #include "content/child/blob_storage/blob_message_filter.h"
@@ -611,6 +613,13 @@ void RenderThreadImpl::Init(
   // Register this object as the main thread.
   ChildProcess::current()->set_main_thread(this);
 
+  // In single process mode we may already have a factory set.
+  if (!base::SingleValueHistogramsFactory::Get()) {
+    base::SingleValueHistogramsFactory::SetFactory(
+        new metrics::SingleValueHistogramsFactoryImpl(
+            GetConnector(), base::ThreadTaskRunnerHandle::Get()));
+  }
+
   gpu_ = ui::Gpu::Create(
       GetConnector(),
       IsRunningInMash() ? ui::mojom::kServiceName : mojom::kBrowserServiceName,