Upstream Chrome on iOS source code [8/11].

ios/chrome/browser/ui/stack_view/card_stack_pinch_gesture_recognizer.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/card_stack_pinch_gesture_recognizer.h"
+
+#include "base/logging.h"
+
+@interface CardStackPinchGestureRecognizer ()
+
+// Returns the number of non-ended, non-cancelled touches in |event|.
+- (NSUInteger)numberOfActiveTouchesInEvent:(UIEvent*)event;
+
+@end
+
+@implementation CardStackPinchGestureRecognizer
+
+@synthesize numberOfActiveTouches = numberOfActiveTouches_;
+
+- (NSUInteger)numberOfActiveTouches {
+  // Certain corner cases can cause |numberOfActiveTouches_| to temporarily
+  // grow to be larger than |[self numberOfTouches]| (this seems to occur only
+  // when the user brings two fingers very closely together). As a safeguard,
+  // ensure that the number returned is never greater than
+  // |[self numberOfTouches]|, as the latter number dictates the greatest index
+  // that a client can pass to |locationOfTouch:| without causing an exception.
+  return std::min(numberOfActiveTouches_, [self numberOfTouches]);
+}
+
+- (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
+  numberOfActiveTouches_ = [self numberOfActiveTouchesInEvent:event];
+  [super touchesBegan:touches withEvent:event];
+}
+
+- (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
+  numberOfActiveTouches_ = [self numberOfActiveTouchesInEvent:event];
+  [super touchesEnded:touches withEvent:event];
+}
+
+- (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
+  numberOfActiveTouches_ = [self numberOfActiveTouchesInEvent:event];
+  [super touchesCancelled:touches withEvent:event];
+}
+
+- (void)reset {
+  numberOfActiveTouches_ = 0;
+  [super reset];
+}
+
+- (NSUInteger)numberOfActiveTouchesInEvent:(UIEvent*)event {
+  NSUInteger count = 0;
+  for (UITouch* touch in [event touchesForGestureRecognizer:self]) {
+    if (touch.phase == UITouchPhaseBegan || touch.phase == UITouchPhaseMoved ||
+        touch.phase == UITouchPhaseStationary)
+      count++;
+  }
+  return count;
+}
+
+@end