Enable smooth scrolling on mac

base/mac/scoped_smooth_scrolling_disabler_mac.mm

Index: base/mac/scoped_smooth_scrolling_disabler_mac.mm
diff --git a/base/mac/scoped_smooth_scrolling_disabler_mac.mm b/base/mac/scoped_smooth_scrolling_disabler_mac.mm
new file mode 100644
index 0000000000000000000000000000000000000000..57c1e723d88f7a6a4b7a01ef3fc43fcdc4208ad2
--- /dev/null
+++ b/base/mac/scoped_smooth_scrolling_disabler_mac.mm
@@ -0,0 +1,26 @@
+// Copyright (c) 2011 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 "base/mac/scoped_smooth_scrolling_disabler_mac.h"
+
+#include <Cocoa/Cocoa.h>
+
+namespace base {
+
+ScopedSmoothScrollingDisabler::ScopedSmoothScrollingDisabler(
+    bool actually_disable) {
+  if (actually_disable) {
+    // With smooth scrolling, cmd-down et al send many small scroll events on a
+    // timer, which is problematic for some tests.
+    [[NSUserDefaults standardUserDefaults]
+        setBool:NO forKey:@"AppleScrollAnimationEnabled"];

[Mark Mentovai, 2011/08/31 02:59:57]

These suck because they leave bad prefs on the disk when the test crashes, which
it will because our tests are sucky. Is there a better way?

[Nico, 2011/08/31 03:30:51]

I couldn't think of one; this is how Apple's DRT does it. I thought it's not too
terrible because
a) most tests shouldn't really care if this is set or not (I even considered
just disabling this early in the test runner, but decided that it's probably
better to run most tests in the shipping configuration)
b) When one of these two tests runs again, the pref gets cleaned up

[Mark Mentovai, 2011/08/31 03:39:01]

My concern is actually the confluence of (a) and (b). “Most” tests “shouldn’t
really” care, meaning that if any test kind of cares, they’ll produce
questionable results that are nearly impossible to diagnose because the pref
won’t be cleaned up until a test that uses this runs again—without crashing.

Humor me and see if this works:

    NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
    scoped_nsobject<NSMutableDictionary> registration_domain =
        [[defaults volatileDomainForName:NSRegistrationDomain] mutableCopy];
    [registration_domain setObject:[NSNumber numberWithBool:NO]
                            forKey:@"AppleScrollAnimationEnabled"];
    [defaults setVolatileDomain:registration_domain
                        forName:NSRegistrationDomain];

+  }
+}
+
+ScopedSmoothScrollingDisabler::~ScopedSmoothScrollingDisabler() {
+  [[NSUserDefaults standardUserDefaults]
+      removeObjectForKey:@"AppleScrollAnimationEnabled"];
+}
+
+}  // namespace base