Add startup metrics that measure the performance of the first web contents.

chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc

Index: chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
diff --git a/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc b/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
index 5ca78d2c878dadfd35ef372b82e66b50e6ab46ac..93c9c70f7f84cda0b6d0a8b79b9b7407fe73d433 100644
--- a/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
+++ b/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
@@ -264,6 +264,12 @@ void ChromeBrowserMainExtraPartsMetrics::PostBrowserStart() {
   UMA_HISTOGRAM_COUNTS_100("Hardware.Display.Count.OnStartup", display_count_);
   gfx::Screen::GetNativeScreen()->AddObserver(this);
   is_screen_observer_ = true;
+
+  if (FirstWebContentsProfiler::ShouldCollectMetrics()) {
+    first_web_contents_profiler_ =
+        FirstWebContentsProfiler::CreateProfilerForFirstWebContents(this)
+            .Pass();
+  }
 }
 
 void ChromeBrowserMainExtraPartsMetrics::OnDisplayAdded(
@@ -281,6 +287,10 @@ void ChromeBrowserMainExtraPartsMetrics::OnDisplayMetricsChanged(
     uint32_t changed_metrics) {
 }
 
+void ChromeBrowserMainExtraPartsMetrics::ProfilerFinishedCollectingMetrics() {
+  first_web_contents_profiler_.reset();
+}
+
 void ChromeBrowserMainExtraPartsMetrics::EmitDisplaysChangedMetric() {
   int display_count = gfx::Screen::GetNativeScreen()->GetNumDisplays();
   if (display_count != display_count_) {