Add comment to not enable impulse scrolling on the Mac

It makes Chromium feel sluggish in scrolling and makes it stand out
but in a bad way.

Bug: none
Change-Id: Ic177125dc9254788fc37ad9992eee6fd19f70aeb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2855037
Commit-Queue: Avi Drissman <avi@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Auto-Submit: Avi Drissman <avi@chromium.org>
Reviewed-by: ccameron <ccameron@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#876800}

cc/base/features.cc

@@ -21,6 +21,10 @@ const base::Feature kAnimatedImageResume = {"AnimatedImageResume",
                                             base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables impulse-style scroll animations in place of the default ones.
+//
+// Note: Do not enable this on the Mac. The animation does not match the system
+// scroll animation curve to such an extent that it makes Chromium stand out in
+// a bad way.
 const base::Feature kImpulseScrollAnimations = {
     "ImpulseScrollAnimations",
     base::FEATURE_DISABLED_BY_DEFAULT};