Perf metric tracking the wallclock time it takes to show a new tab page.

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 0160324883eedd73339f39cf94cd8b127ed0532d..552c252311bded66b0c0f54dd0e38e59ac515267 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -77170,6 +77170,24 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Toolbar.Menu.NewIncognitoTabPresentationDuration" units="ms">
+  <owner>peterlaurens@chromium.org</owner>
+  <summary>
+    The number of millseconds between the user requesting a new incognito tab,
+    e.g. by tapping the New Incognito Tab entry in the main tools menu, and it
+    completing its animation on screen.
+  </summary>
+</histogram>
+
+<histogram name="Toolbar.Menu.NewTabPresentationDuration" units="ms">
+  <owner>peterlaurens@chromium.org</owner>
+  <summary>
+    The number of millseconds between the user requesting a new tab, e.g. by
+    tapping the New Tab entry in the main tools menu, and it completing its
+    animation on screen.
+  </summary>
+</histogram>
+
 <histogram name="Toolbar.ShowToolsMenuResponsiveness" units="ms">
   <owner>peterlaurens@chromium.org</owner>
   <summary>
@@ -77180,6 +77198,25 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Toolbar.TabSwitcher.NewIncognitoTabPresentationDuration"
+    units="ms">
+  <owner>peterlaurens@chromium.org</owner>
+  <summary>
+    The number of millseconds between the user requesting a new incognito tab,
+    from within the tab switcher, e.g. by tapping the New Tab button from the
+    tab switcher UI, and it completing its animation on screen.
+  </summary>
+</histogram>
+
+<histogram name="Toolbar.TabSwitcher.NewTabPresentationDuration" units="ms">
+  <owner>peterlaurens@chromium.org</owner>
+  <summary>
+    The number of millseconds between the user requesting a new tab, from within
+    the tab switcher UI, e.g. by tapping the New Tab button from the tab
+    switcher UI, and it completing its animation on screen.
+  </summary>
+</histogram>
+
 <histogram name="TopSites.NumberOfApplyBlacklist">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>The number of times TopSitesImpl::ApplyBlacklist is called.</summary>