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 3cd25f1ebba73068fdcfec0e57e0bcb32d4fc927..b1a42cbfb8cb2dd3c815c31072d7fbd1da7063e1 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_sample_metrics.mojom.h"
+#include "components/metrics/single_sample_metrics_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"
@@ -393,6 +395,22 @@ bool IsRunningInMash() {
   return cmdline->HasSwitch(switches::kIsRunningInMash);
 }
 
+// Necessary since BindInterface() is a template and can't be bound directly.
+void CreateSingleSampleMetricsProvider(
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+    service_manager::Connector* connector,
+    metrics::mojom::SingleSampleMetricsProviderRequest request) {
+  if (task_runner->BelongsToCurrentThread()) {
+    connector->BindInterface(mojom::kBrowserServiceName, std::move(request));
+    return;
+  }
+
+  task_runner->PostTask(
+      FROM_HERE,
+      base::Bind(&CreateSingleSampleMetricsProvider, std::move(task_runner),
+                 connector, base::Passed(&request)));
+}
+
 }  // namespace
 
 // For measuring memory usage after each task. Behind a command line flag.
@@ -614,6 +632,14 @@ 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::SingleSampleMetricsFactory::Get()) {
+    base::SingleSampleMetricsFactory::SetFactory(
+        new metrics::SingleSampleMetricsFactoryImpl(base::BindRepeating(

[Alexei Svitkine (slow), 2017/05/03 21:18:48]

Hmm, it seems strange that this is constructing an Impl object from the metrics
component. Impl sounds like it's implementation detail that shouldn't be exposed
outside the component.

How about keeping _impl.h private to the component and having a helper function
in metrics component that returns the instance?

[DaleCurtis, 2017/05/03 21:37:52]

You mean something like a "static
metrics::InitializeSingleSampleMetrics(callback)" ?

[Alexei Svitkine (slow), 2017/05/03 21:45:08]

Yep!

[DaleCurtis, 2017/05/04 02:28:59]

Done.

[Alexei Svitkine (slow), 2017/05/04 14:15:08]

Hmm, did you forget to upload a patchset? Don't see this part of the change...

[DaleCurtis, 2017/05/04 18:55:27]

No intentionally didn't upload since it was busted but forgot I posted this.
Fixed in latest patch set.

+            &CreateSingleSampleMetricsProvider, message_loop()->task_runner(),
+            GetConnector())));
+  }
+
   gpu_ = ui::Gpu::Create(
       GetConnector(),
       IsRunningInMash() ? ui::mojom::kServiceName : mojom::kBrowserServiceName,