Add UMA metric: Startup.BrowserMainToRendererMain.

content/renderer/renderer_main.cc

Index: content/renderer/renderer_main.cc
diff --git a/content/renderer/renderer_main.cc b/content/renderer/renderer_main.cc
index 0f44527057216b3d05a7a47b1d316e739f2894a1..ea7c913adfb26058120daa11d6786648cf9b1495 100644
--- a/content/renderer/renderer_main.cc
+++ b/content/renderer/renderer_main.cc
@@ -16,9 +16,11 @@
 #include "base/strings/string_util.h"
 #include "base/sys_info.h"
 #include "base/threading/platform_thread.h"
+#include "base/time/time.h"
 #include "base/timer/hi_res_timer_manager.h"
 #include "base/trace_event/trace_event.h"
 #include "components/scheduler/renderer/renderer_scheduler.h"
+#include "components/startup_metric_utils/common/startup_metric_messages.h"
 #include "content/child/child_process.h"
 #include "content/common/content_constants_internal.h"
 #include "content/public/common/content_switches.h"
@@ -82,6 +84,8 @@ int RendererMain(const MainFunctionParams& parameters) {
   // expect synchronous events around the main loop of a thread.
   TRACE_EVENT_ASYNC_BEGIN0("startup", "RendererMain", 0);
 
+  const base::TimeTicks renderer_main_entry_time = base::TimeTicks::Now();
+
   base::trace_event::TraceLog::GetInstance()->SetProcessName("Renderer");
   base::trace_event::TraceLog::GetInstance()->SetProcessSortIndex(
       kTraceEventRendererProcessSortIndex);
@@ -200,6 +204,10 @@ int RendererMain(const MainFunctionParams& parameters) {
     RenderThreadImpl::Create(main_message_loop.Pass(),
                              renderer_scheduler.Pass());
 #endif
+    RenderThreadImpl::current()->Send(
+        new StartupMetricHostMsg_RecordRendererMainEntryTime(
+            renderer_main_entry_time));
+
     base::HighResolutionTimerManager hi_res_timer_manager;
 
     if (run_loop) {