Adding tools menu responsiveness metric.

ios/chrome/browser/ui/browser_view_controller.mm

Index: ios/chrome/browser/ui/browser_view_controller.mm
diff --git a/ios/chrome/browser/ui/browser_view_controller.mm b/ios/chrome/browser/ui/browser_view_controller.mm
index 1271cea016bb063baa8cc2dd4162d3f0fff7faca..d24e44201cdf03d08721b9b8929c73938739b21b 100644
--- a/ios/chrome/browser/ui/browser_view_controller.mm
+++ b/ios/chrome/browser/ui/browser_view_controller.mm
@@ -3384,6 +3384,22 @@ class BrowserBookmarkModelBridge : public bookmarks::BookmarkModelObserver {
   DCHECK(_browserState);
   DCHECK(self.visible || self.dismissingModal);
 
+  // Record the responsiveness of this show menu operation.
+  NSTimeInterval startTime = [NSDate timeIntervalSinceReferenceDate];

[rohitrao (ping after 24h), 2017/05/18 01:16:25]

Another option would be to add this startTime to ToolsMenuConfiguration and read
it from there when the animation completes.  It's not really menu configuration
data, but it would simplify the logic a bit and avoid adding a new notification.
 It's also a bit safer if we ever fail to run the toolsmenu animation for some
reason, since we wouldn't have a block that could leak.

Thoughts?  Which do you prefer?

[PL, 2017/05/18 23:36:34]

Done! This is a smart idea... the configuration isn't stored anywhere at
present, but I can just store the value from the configuration in the view
controller and use it.

I do think this will result in a smaller amount of code... although it does
introduce two instance variables purely for the use of metrics (whereas before I
had none, if you consider the 'didShow' notification could be used for something
non-metric related).

+  __block id<NSObject> oneTimeObserver = [[NSNotificationCenter defaultCenter]
+      addObserverForName:kMenuDidShowNotification
+                  object:nil
+                   queue:nil
+              usingBlock:^(NSNotification* _Nonnull note) {
+                UMA_HISTOGRAM_TIMES(
+                    "UI.Performance.ShowToolsMenuResponsiveness",
+                    base::TimeDelta::FromSecondsD(
+                        [NSDate timeIntervalSinceReferenceDate] - startTime));
+                [[NSNotificationCenter defaultCenter]
+                    removeObserver:oneTimeObserver];
+                oneTimeObserver = nil;
+              }];
+
   // Dismiss the omnibox (if open).
   [_toolbarController cancelOmniboxEdit];
   // Dismiss the soft keyboard (if open).