Upstream Chrome on iOS source code [9/11].

ios/chrome/browser/ui/tab_switcher/tab_switcher_button.mm

+// Copyright 2016 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/tab_switcher/tab_switcher_button.h"
+
+#include "base/mac/scoped_nsobject.h"
+#import "ios/third_party/material_components_ios/src/components/Ink/src/MaterialInk.h"
+
+@interface TabSwitcherButton () {
+  base::scoped_nsobject<MDCInkTouchController> _inkTouchController;
+}
+@end
+
+@implementation TabSwitcherButton
+
+- (instancetype)initWithFrame:(CGRect)frame {
+  self = [super initWithFrame:frame];
+  if (self) {
+    _inkTouchController.reset(
+        [[MDCInkTouchController alloc] initWithView:self]);
+    [_inkTouchController addInkView];
+    // TODO(crbug.com/606807): Adjust the desired ink color.
+    [_inkTouchController defaultInkView].inkColor =
+        [[UIColor whiteColor] colorWithAlphaComponent:0.4];
+  }
+  return self;
+}
+
+- (void)resetState {
+  [_inkTouchController cancelInkTouchProcessing];
+}
+
+@end