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

ios/chrome/browser/ui/stack_view/stack_view_controller.mm

 // Copyright 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.
 
 #import "ios/chrome/browser/ui/stack_view/stack_view_controller.h"
 
 #import <QuartzCore/QuartzCore.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 2007 matching lines @@
 
   if (parentView) {
     CGPoint viewCoordinate = [parentView convertPoint:center toView:self.view];
     _lastTapPoint = viewCoordinate;
   }
 }
 
 - (Tab*)dismissWithNewTabAnimation:(const GURL&)URL
                            atIndex:(NSUInteger)position
                         transition:(ui::PageTransition)transition {
+  // Record the start time for this operation so it may be reported as a metric
+  // in the animation completion block.
+  NSTimeInterval startTime = [NSDate timeIntervalSinceReferenceDate];
+
   // This helps smooth out the animation.
   [[_scrollView layer] setShouldRasterize:YES];
   if (_isBeingDismissed)
     return NULL;
   DCHECK(_isActive);
   [self prepareForDismissal];
   _isBeingDismissed = YES;
   [self setNeedsStatusBarAppearanceUpdate];
   DCHECK(URL.is_valid());
   // Stop pre-loading cards.
@@ skipping 32 matching lines @@
   newCard.image = [tab updateSnapshotWithOverlay:YES visibleFrameOnly:YES];
   [tab view].frame = originalTabFrame;
   newCard.center =
       CGPointMake(CGRectGetMidX(viewBounds), CGRectGetMidY(viewBounds));
   [self.view addSubview:newCard];
 
   void (^completionBlock)(void) = ^{
     [newCard removeFromSuperview];
     [[_scrollView layer] setShouldRasterize:NO];
     [_delegate tabSwitcherDismissTransitionDidEnd:self];
+    double duration = [NSDate timeIntervalSinceReferenceDate] - startTime;
+    if (_activeCardSet.tabModel.isOffTheRecord) {
+      UMA_HISTOGRAM_TIMES(
+          "Toolbar.TabSwitcher.NewIncognitoTabPresentationDurationn",
+          base::TimeDelta::FromSecondsD(duration));
+    } else {
+      UMA_HISTOGRAM_TIMES("Toolbar.TabSwitcher.NewTabPresentationDuration",
+                          base::TimeDelta::FromSecondsD(duration));
+    }
   };
 
   CGPoint origin = _lastTapPoint;
   _lastTapPoint = CGPointZero;
   ios_internal::page_animation_util::AnimateInPaperWithAnimationAndCompletion(
       newCard, -statusBarHeight,
       newCard.frame.size.height - newCard.image.size.height, origin,
       [self isCurrentSetIncognito], nil, completionBlock);
   // TODO(stuartmorgan): Animate the other set off to the side.
 
@@ skipping 1413 matching lines @@
 
 @end
 
 @implementation StackViewController (Testing)
 
 - (UIScrollView*)scrollView {
   return _scrollView.get();
 }
 
 @end