Make scrollAnimatorEnabled work on Mac like it does on other platforms

ui/gfx/animation/animation_mac.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 "ui/gfx/animation/animation.h"
+
+#include "base/mac/mac_util.h"
+#include "base/message_loop/message_loop.h"
+
+namespace gfx {
+
+// static
+bool Animation::ScrollAnimationsEnabledBySystem() {
+  // Because of sandboxing, OS settings should only be queried from the browser
+  // process.
+  DCHECK(base::MessageLoopForUI::IsCurrent() ||
+      base::MessageLoopForIO::IsCurrent());
+
+  bool enabled = false;
+  id value = nil;
+  if (base::mac::IsOSMountainLionOrLater()) {
+    value = [[NSUserDefaults standardUserDefaults]
+        objectForKey:@"NSScrollAnimationEnabled"];
+  } else {
+    value = [[NSUserDefaults standardUserDefaults]
+        objectForKey:@"AppleScrollAnimationEnabled"];
+  }
+  if (value)
+    enabled = [value boolValue];
+  return enabled;
+}
+
+} // namespace gfx