Add new histograms to measure time in PreMainMessageLoop.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 64db27be2722374cf46243c062376ed18c80159b..21838a3def225c614c7e45e6bd6882ac5640ff2e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -36871,6 +36871,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Startup.BrowserProcessImpl_PreMainMessageLoopRunTime"
+    units="milliseconds">
+  <owner>rkaplow@chromium.org</owner>
+  <summary>
+    The amount of time that elapsed during
+    BrowserProcessImpl::PreMainMessageLoopRun.
+  </summary>
+</histogram>
+
 <histogram name="Startup.BrowserWindowDisplay" units="milliseconds">
   <owner>jeremy@chromium.org</owner>
   <summary>
@@ -37086,6 +37095,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Startup.PreMainMessageLoopRunImplTime" units="milliseconds">
+  <owner>rkaplow@chromium.org</owner>
+  <summary>
+    The amount of time that elapsed during
+    ChromeBrowserMainParts::PreMainMessageLoopRunImpl.
+  </summary>
+</histogram>
+
 <histogram name="Startup.ShowAppListColdStart" units="milliseconds">
   <owner>jeremy@chromium.org</owner>
   <owner>tapted@chromium.org</owner>
@@ -37190,6 +37207,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Startup.StartupBrowserCreator_ProcessCmdLineImplTime"
+    units="milliseconds">
+  <owner>rkaplow@chromium.org</owner>
+  <summary>
+    The amount of time that elapsed during
+    StartupBrowserCreator::ProcessCmdLineImpl.
+  </summary>
+</histogram>
+
 <histogram name="Startup.WarmStartTimeFromRemoteProcessStart"
     units="milliseconds">
   <owner>jeremy@chromium.org</owner>