Add a RWH_TabSwitchPaintDuration histogram.

chrome/browser/renderer_host/render_widget_host_view_gtk.cc

Index: chrome/browser/renderer_host/render_widget_host_view_gtk.cc
diff --git a/chrome/browser/renderer_host/render_widget_host_view_gtk.cc b/chrome/browser/renderer_host/render_widget_host_view_gtk.cc
index b54aba3e9e2749c8fe9e96e301162ee6495189f7..b19cb46e66f3e424a4bcc0dbfa2f8606d122c23e 100644
--- a/chrome/browser/renderer_host/render_widget_host_view_gtk.cc
+++ b/chrome/browser/renderer_host/render_widget_host_view_gtk.cc
@@ -376,6 +376,8 @@ void RenderWidgetHostViewGtk::DidBecomeSelected() {
   if (!is_hidden_)
     return;
 
+  if (tab_switch_paint_time_.is_null())
+    tab_switch_paint_time_ = base::TimeTicks::Now();
   is_hidden_ = false;
   host_->WasRestored();
 }
@@ -595,6 +597,15 @@ void RenderWidgetHostViewGtk::Paint(const gfx::Rect& damage_rect) {
       // time the backing store is NULL...
       whiteout_start_time_ = base::TimeTicks();
     }
+    if (!tab_switch_paint_time_.is_null()) {
+      base::TimeDelta tab_switch_paint_duration = base::TimeTicks::Now() -
+          tab_switch_paint_time_;
+      UMA_HISTOGRAM_TIMES("MPArch.RWH_TabSwitchPaintDuration",
+          tab_switch_paint_duration);
+      // Reset tab_switch_paint_time_ to 0 so future tab selections are
+      // recorded.
+      tab_switch_paint_time_ = base::TimeTicks();
+    }
   } else {
     if (window)
       gdk_window_clear(window);