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

ios/chrome/browser/ui/browser_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/browser_view_controller.h"
 
 #import <AssetsLibrary/AssetsLibrary.h>
 #import <MobileCoreServices/MobileCoreServices.h>
 #import <PassKit/PassKit.h>
 #import <Photos/Photos.h>
@@ skipping 554 matching lines @@
 @property(nonatomic, assign, getter=isInNewTabAnimation) BOOL inNewTabAnimation;
 // Whether BVC prefers to hide the status bar. This value is used to determine
 // the response from the |prefersStatusBarHidden| method.
 @property(nonatomic, assign) BOOL hideStatusBar;
 // Whether the VoiceSearchBar should be displayed.
 @property(nonatomic, readonly) BOOL shouldShowVoiceSearchBar;
 // Coordinator for displaying a modal overlay with activity indicator to prevent
 // the user from interacting with the browser view.
 @property(nonatomic, strong)
     ActivityOverlayCoordinator* activityOverlayCoordinator;
+// A block to be run when the |tabWasAdded:| method completes the animation
+// for the presentation of a new tab. Can be used to record performance metrics.
+@property(nonatomic, strong, nullable)
+    ProceduralBlock foregroundTabWasAddedCompletionBlock;
 
 // The user agent type used to load the currently visible page. User agent type
 // is NONE if there is no visible page or visible page is a native page.
 @property(nonatomic, assign, readonly) web::UserAgentType userAgentType;
 
 // Returns the header views, all the chrome on top of the page, including the
 // ones that cannot be scrolled off screen by full screen.
 @property(nonatomic, strong, readonly) NSArray<HeaderDefinition*>* headerViews;
 
 // BVC initialization:
@@ skipping 340 matching lines @@
 
 @synthesize contentArea = _contentArea;
 @synthesize typingShield = _typingShield;
 @synthesize active = _active;
 @synthesize visible = _visible;
 @synthesize viewVisible = _viewVisible;
 @synthesize dismissingModal = _dismissingModal;
 @synthesize hideStatusBar = _hideStatusBar;
 @synthesize activityOverlayCoordinator = _activityOverlayCoordinator;
 @synthesize presenting = _presenting;
+@synthesize foregroundTabWasAddedCompletionBlock =
+    _foregroundTabWasAddedCompletionBlock;
 
 #pragma mark - Object lifecycle
 
 - (instancetype)initWithTabModel:(TabModel*)model
                     browserState:(ios::ChromeBrowserState*)browserState
                dependencyFactory:
                    (BrowserViewControllerDependencyFactory*)factory {
   self = [super initWithNibName:nil bundle:base::mac::FrameworkBundle()];
   if (self) {
     DCHECK(factory);
@@ skipping 246 matching lines @@
   [self setNeedsStatusBarAppearanceUpdate];
 }
 
 #pragma mark - IBActions
 
 - (void)shieldWasTapped:(id)sender {
   [_toolbarController cancelOmniboxEdit];
 }
 
 - (void)newTab:(id)sender {
+  // Observe the timing of the new tab creation, both MainController
+  // and BrowserViewController call into this method on the correct BVC to
+  // create new tabs making it preferable to doing this in
+  // |chromeExecuteCommand:|.
+  NSTimeInterval startTime = [NSDate timeIntervalSinceReferenceDate];
+  BOOL offTheRecord = self.isOffTheRecord;
+  self.foregroundTabWasAddedCompletionBlock = ^{
+    double duration = [NSDate timeIntervalSinceReferenceDate] - startTime;

[Ilya Sherman, 2017/05/23 22:55:22]

Optional nit: Mebbe define a TimeDelta here, outside the if/else

[PL, 2017/06/08 17:57:47]

Done!

+    if (offTheRecord) {
+      UMA_HISTOGRAM_TIMES("Toolbar.Menu.NewIncognitoTabPresentationDuration",
+                          base::TimeDelta::FromSecondsD(duration));
+    } else {
+      UMA_HISTOGRAM_TIMES("Toolbar.Menu.NewTabPresentationDuration",
+                          base::TimeDelta::FromSecondsD(duration));
+    }
+  };
+
   [self setLastTapPoint:sender];
   DCHECK(self.visible || self.dismissingModal);
   Tab* currentTab = [_model currentTab];
   if (currentTab) {
     [currentTab updateSnapshotWithOverlay:YES visibleFrameOnly:YES];
   }
   [self addSelectedTabWithURL:GURL(kChromeUINewTabURL)
                    transition:ui::PAGE_TRANSITION_TYPED];
 }
 
@@ skipping 407 matching lines @@
           // Use the model's currentTab here because it is possible that it can
           // be reset to a new value before the new Tab animation finished (e.g.
           // if another Tab shows a dialog via |dialogPresenter|). However, that
           // tab's view hasn't been displayed yet because it was in a new tab
           // animation.
           Tab* currentTab = [_model currentTab];
           if (currentTab) {
             [self tabSelected:currentTab];
           }
           startVoiceSearchIfNecessaryBlock();
+
+          if (self.foregroundTabWasAddedCompletionBlock) {
+            self.foregroundTabWasAddedCompletionBlock();
+          }
         });
   } else {
     // -updateSnapshotWithOverlay will force a screen redraw, so take the
     // snapshot before adding the views needed for the background animation.
     Tab* topTab = [_model currentTab];
     UIImage* image = [topTab updateSnapshotWithOverlay:YES
                                       visibleFrameOnly:self.isToolbarOnScreen];
     // Add three layers in order on top of the contentArea for the animation:
     // 1. The black "background" screen.
     UIView* background = [[UIView alloc] initWithFrame:[_contentArea bounds]];
@@ skipping 18 matching lines @@
           self.inNewTabAnimation = NO;
           // Resnapshot the top card if it has its own toolbar, as the toolbar
           // will be captured in the new tab animation, but isn't desired for
           // the stack view snapshots.
           id nativeController = [self nativeControllerForTab:topTab];
           if ([nativeController conformsToProtocol:@protocol(ToolbarOwner)])
             [topTab updateSnapshotWithOverlay:YES visibleFrameOnly:YES];
           startVoiceSearchIfNecessaryBlock();
         });
   }
+  // Reset the foreground tab completion block so that it can never be
+  // called more than once regardless of foreground/background tab appearances.
+  self.foregroundTabWasAddedCompletionBlock = nil;
 }
 
 #pragma mark - UI Configuration and Layout
 
 - (void)updateWithTabModel:(TabModel*)model
               browserState:(ios::ChromeBrowserState*)browserState {
   DCHECK(model);
   DCHECK(browserState);
   DCHECK(!_model);
   DCHECK(!_browserState);
@@ skipping 3499 matching lines @@
 
 - (UIView*)voiceSearchButton {
   return _voiceSearchButton;
 }
 
 - (id<LogoAnimationControllerOwner>)logoAnimationControllerOwner {
   return [self currentLogoAnimationControllerOwner];
 }
 
 @end