Add scrolling metrics in grid views

This CL adds metrics to track scrolling actions in grid views:
- events when the user scrolls;
- cumulative time spent scrolling.

Fixed: 1439234
Change-Id: Id5e5c3bb0739359ddd6670f4de10789c3c25ca35
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4466313
Auto-Submit: Louis Romero <lpromero@google.com>
Reviewed-by: Aliona Dangla <alionadangla@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Louis Romero <lpromero@google.com>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1136168}

ios/chrome/browser/ui/tab_switcher/tab_grid/grid/grid_view_controller.mm

@@ -5,6 +5,7 @@
 #import "ios/chrome/browser/ui/tab_switcher/tab_grid/grid/grid_view_controller.h"
 
 #import <algorithm>
+#import <memory>
 
 #import "base/check_op.h"
 #import "base/ios/block_types.h"
@@ -56,6 +57,18 @@
 #error "This file requires ARC support."
 #endif
 
+class ScrollingTimeLogger {
+ public:
+  ScrollingTimeLogger() : start_(base::TimeTicks::Now()) {}
+  ~ScrollingTimeLogger() {
+    base::TimeDelta duration = base::TimeTicks::Now() - start_;
+    base::UmaHistogramTimes("IOS.TabSwitcher.TimeSpentScrolling", duration);
+  }
+
+ private:
+  base::TimeTicks start_;
+};
+
 namespace {
 
 // Constants used in the spring animation when inserting items in the thumb
@@ -171,10 +184,13 @@ @interface GridViewController () <GridCellDelegate,
 @property(nonatomic, assign) NSInteger inactiveTabsDaysThreshold;
 // Tracks if a drop action initiated in this grid is in progress.
 @property(nonatomic) BOOL localDragActionInProgress;
-
 @end
 
-@implementation GridViewController
+@implementation GridViewController {
+  // Tracks when the grid view is scrolling. Create a new instance to start
+  // timing and reset to stop and log the associated time histogram.
+  std::unique_ptr<ScrollingTimeLogger> _scrollingTimeLogger;
+}
 
 @synthesize thumbStripEnabled = _thumbStripEnabled;
 
@@ -1099,6 +1115,23 @@ - (void)scrollViewDidScroll:(UIScrollView*)scrollView {
 
 - (void)scrollViewWillBeginDragging:(UIScrollView*)scrollView {
   [self.delegate gridViewControllerWillBeginDragging:self];
+  base::RecordAction(base::UserMetricsAction("MobileTabGridUserScrolled"));
+  _scrollingTimeLogger = std::make_unique<ScrollingTimeLogger>();
+}
+
+- (void)scrollViewDidEndDragging:(UIScrollView*)scrollView
+                  willDecelerate:(BOOL)decelerate {
+  if (!decelerate) {
+    _scrollingTimeLogger = nullptr;
+  }
+}
+
+- (void)scrollViewDidEndDecelerating:(UIScrollView*)scrollView {
+  _scrollingTimeLogger = nullptr;
+}
+
+- (void)scrollViewDidScrollToTop:(UIScrollView*)scrollView {
+  base::RecordAction(base::UserMetricsAction("MobileTabGridUserScrolledToTop"));
 }
 
 - (void)scrollViewDidChangeAdjustedContentInset:(UIScrollView*)scrollView {

tools/metrics/actions/actions.xml

@@ -21817,6 +21817,23 @@ should be able to be added at any place in this file.
   </description>
 </action>
 
+<action name="MobileTabGridUserScrolled">
+  <owner>lpromero@chromium.org</owner>
+  <owner>alionadangla@chromium.org</owner>
+  <owner>chromeleon@google.com</owner>
+  <description>User in the iOS tab grid scrolled the grid of tabs.</description>
+</action>
+
+<action name="MobileTabGridUserScrolledToTop">
+  <owner>lpromero@chromium.org</owner>
+  <owner>alionadangla@chromium.org</owner>
+  <owner>chromeleon@google.com</owner>
+  <description>
+    User in the iOS tab grid tapped the status bar to scroll to the top of the
+    grid of tabs.
+  </description>
+</action>
+
 <action name="MobileTabNewTab">
   <owner>ewannpv@chromium.org</owner>
   <owner>gambard@chromium.org</owner>

tools/metrics/histograms/metadata/ios/histograms.xml

@@ -2347,6 +2347,17 @@ chromium-metrics-reviews@google.com.
   </summary>
 </histogram>
 
+<histogram name="IOS.TabSwitcher.TimeSpentScrolling" units="ms"
+    expires_after="2024-05-14">
+  <owner>lpromero@chromium.org</owner>
+  <owner>alionadangla@chromium.org</owner>
+  <owner>chromeleon@google.com</owner>
+  <summary>
+    The time spent while the tab grid is scrolled by the user. This includes the
+    deceleration time.
+  </summary>
+</histogram>
+
 <histogram name="IOS.TextSelection.EntityDetection.DetectedEntityType"
     enum="TextSelectionDetectedEntityType" expires_after="2023-10-08">
   <owner>rajendrant@chromium.org</owner>