Add haptic feedback for swipe-to-go-back.

ios/chrome/browser/ui/side_swipe/side_swipe_navigation_view.mm

 // Copyright 2015 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/side_swipe/side_swipe_navigation_view.h"
 
 #include <cmath>
 
 #include "base/logging.h"
 #include "base/mac/objc_property_releaser.h"
@@ skipping 48 matching lines @@
 
 // The final scale of the selection bubble when the threshold is met.
 const CGFloat kSelectionAnimationScale = 23;
 
 // The duration of the animations played when the threshold is met.
 const CGFloat kSelectionAnimationDuration = 0.5;
 }
 
 @interface SideSwipeNavigationView () {
  @private
+  // Has the current swipe gone past the point where the action would trigger?
+  // Will be reset to NO if it recedes before that point (ie, not a latch).
+  BOOL thresholdTriggered_;
 
   // The back or forward sprite image.
   base::scoped_nsobject<UIImageView> arrowView_;
 
   // The selection bubble.
   CAShapeLayer* selectionCircleLayer_;
 
   // If |NO| this is an edge gesture and navigation isn't possible. Don't show
   // arrows and bubbles and don't allow navigate.
   BOOL canNavigate_;
@@ skipping 124 matching lines @@
   // Animate selection bubbles dpending on distance.
   [UIView beginAnimations:@"transform" context:NULL];
   [UIView setAnimationDuration:kSelectionSnappingAnimationDuration];
   if (distance < (width * kSwipeThreshold)) {
     // Scale selection down.
     selectionCircleLayer_.transform =
         CATransform3DMakeScale(kSelectionDownScale, kSelectionDownScale, 1);
     selectionCircleLayer_.opacity = 0;
     [arrowView_ setAlpha:MapValueToRange({0, 64}, {0, 1}, distance)];
     [arrowView_ setTintColor:[UIColor whiteColor]];
+    thresholdTriggered_ = NO;
   } else {
     selectionCircleLayer_.transform = CATransform3DMakeScale(1, 1, 1);
     selectionCircleLayer_.opacity = 0.75;
     [arrowView_ setAlpha:1];
     [arrowView_ setTintColor:self.backgroundColor];
+    // Trigger a small haptic blip when exceeding the threshold and mark
+    // such that only one blip gets triggered.
+    if (!thresholdTriggered_) {
+      TriggerHapticFeedbackForSelectionChange();
+      thresholdTriggered_ = YES;
+    }
   }
   [UIView commitAnimations];
 }
 
 - (void)explodeSelection:(void (^)(void))block {
   [CATransaction begin];
   [CATransaction setCompletionBlock:^{
     // Note that the animations below may complete at slightly different times
     // resulting in frame(s) between animation completion and the transaction's
     // completion handler that show the original state. To avoid this flicker,
@@ skipping 94 matching lines @@
 
   if (gesture.state == UIGestureRecognizerStateEnded ||
       gesture.state == UIGestureRecognizerStateCancelled ||
       gesture.state == UIGestureRecognizerStateFailed) {
     CGFloat threshold = width * kSwipeThreshold;
     CGFloat finalDistance = distance + velocityOffset;
     // Ensure the actual distance traveled has met the minimum arrow threshold
     // and that the distance including expected velocity is over |threshold|.
     if (distance > kArrowThreshold && finalDistance > threshold &&
         canNavigate_ && gesture.state == UIGestureRecognizerStateEnded) {
+      TriggerHapticFeedbackForAction();
+
       // Speed up the animation for higher velocity swipes.
       CGFloat animationTime = MapValueToRange(
           {threshold, width},
           {kSelectionAnimationDuration, kSelectionAnimationDuration / 2},
           finalDistance);
       [self animateTargetViewCompleted:YES
                          withDirection:gesture.direction
                           withDuration:animationTime];
       [self explodeSelection:onOverThresholdCompletion];
       if (IsSwipingForward(gesture.direction)) {
         base::RecordAction(base::UserMetricsAction(
             "MobileEdgeSwipeNavigationForwardCompleted"));
       } else {
         base::RecordAction(
             base::UserMetricsAction("MobileEdgeSwipeNavigationBackCompleted"));
       }
     } else {
       [self animateTargetViewCompleted:NO
                          withDirection:gesture.direction
                           withDuration:0.1];
       onUnderThresholdCompletion();
       if (IsSwipingForward(gesture.direction)) {
         base::RecordAction(base::UserMetricsAction(
             "MobileEdgeSwipeNavigationForwardCancelled"));
       } else {
         base::RecordAction(
             base::UserMetricsAction("MobileEdgeSwipeNavigationBackCancelled"));
       }
     }
+    thresholdTriggered_ = NO;
   }
 }
 
 - (void)animateTargetViewCompleted:(BOOL)completed
                      withDirection:(UISwipeGestureRecognizerDirection)direction
                       withDuration:(CGFloat)duration {
   void (^animationBlock)(void) = ^{
     CGRect targetFrame = self.targetView.frame;
     CGRect frame = self.frame;
     CGFloat width = CGRectGetWidth(self.targetView.bounds);
@@ skipping 44 matching lines @@
   selectionCircleLayer.opacity = 0;
   selectionCircleLayer.transform =
       CATransform3DMakeScale(kSelectionDownScale, kSelectionDownScale, 1);
   selectionCircleLayer.path =
       [[UIBezierPath bezierPathWithOvalInRect:bounds] CGPath];
 
   return selectionCircleLayer;
 }
 
 @end