[SlowReport]: Add tracing sampling profiler to renderer process.

Instantiate TracingSamplerProfiler in RendererMain.

Change-Id: I527be13dcff3a58a4e60c8fe8ca21474515b91b0
Reviewed-on: https://chromium-review.googlesource.com/c/1336075Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: oysteine <oysteine@chromium.org>
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613178}

content/renderer/BUILD.gn

@@ -627,6 +627,7 @@ target(link_target_type, "renderer") {
     "//components/metrics",
     "//components/metrics:single_sample_metrics",
     "//components/services/leveldb/public/cpp",
+    "//components/tracing",
     "//components/url_formatter",
     "//components/viz/client",
     "//components/viz/common",

content/renderer/DEPS

@@ -5,6 +5,7 @@ include_rules = [
   "+components/metrics",
   "+components/metrics:single_sample_metrics",
   "+components/payments",
+  "+components/tracing",
   "+components/url_formatter",
   "+components/viz/client",
   "+components/viz/common",

content/renderer/renderer_main.cc

@@ -24,6 +24,7 @@
 #include "base/timer/hi_res_timer_manager.h"
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
+#include "components/tracing/common/tracing_sampler_profiler.h"
 #include "content/common/content_constants_internal.h"
 #include "content/common/content_switches_internal.h"
 #include "content/common/service_manager/service_manager_connection_impl.h"
@@ -210,6 +211,11 @@ int RendererMain(const MainFunctionParams& parameters) {
     new RenderThreadImpl(run_loop.QuitClosure(),
                          std::move(main_thread_scheduler));
 
+    // Setup tracing sampler profiler as early as possible.
+    auto tracing_sampler_profiler =
+        tracing::TracingSamplerProfiler::CreateOnMainThread();
+    tracing_sampler_profiler->OnMessageLoopStarted();
+
     if (need_sandbox)
       should_run_loop = platform.EnableSandbox();