[Merge M48] Add Startup.TimeSinceLastStartup histogram.

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index 920bb2ca8501037d3d5956df34bf2cace2f56d35..daed827e83b4a3ce6c49c4eae6129421ce104147 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -769,6 +769,9 @@ void ChromeBrowserMainParts::RecordBrowserStartupTime() {
   // Record collected startup metrics.
   startup_metric_utils::RecordBrowserMainMessageLoopStart(
       base::TimeTicks::Now(), is_first_run);
+
+  startup_metric_utils::RecordTimeSinceLastStartup(
+      g_browser_process->local_state());
 }
 
 // -----------------------------------------------------------------------------