Upstream Chrome on iOS source code [6/11].

ios/chrome/browser/ui/ntp/recent_tabs/views/disclosure_view.mm

+// Copyright 2014 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.
+
+#include "ios/chrome/browser/ui/ntp/recent_tabs/views/disclosure_view.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace {
+
+// Animation duration for rotating the disclosure icon.
+const NSTimeInterval kDisclosureIconRotateDuration = 0.25;
+
+// Angles of the closure icon.
+// The rotation animation privileges rotating using the smallest angle. Setting
+// |kCollapsedIconAngle| to a value slightly less then 0 forces the animation to
+// always happen in the same half-plane.
+const CGFloat kCollapsedIconAngle = -0.00001;
+const CGFloat kExpandedIconAngle = M_PI;
+
+}  // anonymous namespace
+
+@implementation DisclosureView
+
+- (instancetype)init {
+  UIImage* arrowImage = [[UIImage imageNamed:@"ntp_opentabs_recent_arrow"]
+      imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
+  self = [super initWithImage:arrowImage];
+  return self;
+}
+
+- (void)setTransformWhenCollapsed:(BOOL)collapsed animated:(BOOL)animated {
+  CGFloat angle = collapsed ? kCollapsedIconAngle : kExpandedIconAngle;
+  if (animated) {
+    [UIView animateWithDuration:kDisclosureIconRotateDuration
+                     animations:^{
+                       self.transform = CGAffineTransformRotate(
+                           CGAffineTransformIdentity, angle);
+                     }];
+  } else {
+    self.transform = CGAffineTransformRotate(CGAffineTransformIdentity, angle);
+  }
+}
+
+@end