Add uma histogram for tab scrubbing

chrome/browser/ui/views/ash/tab_scrubber.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/views/ash/tab_scrubber.h"
 
 #include "ash/shell.h"
 #include "ash/wm/window_util.h"
+#include "base/metrics/histogram.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/browser/ui/views/frame/browser_view.h"
 #include "chrome/browser/ui/views/immersive_mode_controller.h"
 #include "chrome/browser/ui/views/tabs/tab.h"
 #include "chrome/browser/ui/views/tabs/tab_strip.h"
 #include "chrome/common/chrome_notification_types.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_source.h"
@@ skipping 235 matching lines @@
   activate_timer_.Stop();
 
   if (browser_ && browser_->window()) {
     BrowserView* browser_view =
         BrowserView::GetBrowserViewForNativeWindow(
             browser_->window()->GetNativeWindow());
     TabStrip* tab_strip = browser_view->tabstrip();
     if (activate && highlighted_tab_ != -1) {
       Tab* tab = tab_strip->tab_at(highlighted_tab_);
       tab->hover_controller()->HideImmediately();
+      int distance =
+          std::abs(
+              highlighted_tab_ - browser_->tab_strip_model()->active_index());
+      UMA_HISTOGRAM_CUSTOM_COUNTS("TabScrubber.Distance", distance, 0, 20, 20);
       browser_->tab_strip_model()->ActivateTabAt(highlighted_tab_, true);
     }
     tab_strip->RemoveObserver(this);
     if (!cancel_immersive_reveal_timer_.IsRunning() &&
         should_cancel_immersive_reveal_) {
       cancel_immersive_reveal_timer_.Start(
           FROM_HERE,
           base::TimeDelta::FromMilliseconds(kCancelImmersiveRevelDelayMS),
           base:: Bind(&TabScrubber::CancelImmersiveReveal,
                       weak_ptr_factory_.GetWeakPtr()));
     }
   }
   swipe_x_ = -1;
   swipe_y_ = -1;
   scrubbing_ = false;
   highlighted_tab_ = -1;
 }
 
 void TabScrubber::CancelImmersiveReveal() {
   cancel_immersive_reveal_timer_.Stop();
   if (browser_ && should_cancel_immersive_reveal_) {
     BrowserView* browser_view =
         BrowserView::GetBrowserViewForNativeWindow(
             browser_->window()->GetNativeWindow());
     browser_view->immersive_mode_controller()->CancelReveal();
   }
   should_cancel_immersive_reveal_ = false;
 }