Extend expiration of smooth-scrolling flag

The work to implement this as a proper option in the UI is still
pending. Until then, this flag is the only mechanism available for
this accessibility option.

Bug: 817814
Change-Id: I18d1d2d62071e85b1be5f6b017cb2b05271795df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2356190Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Adam Goode <agoode@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798218}

chrome/browser/flag-metadata.json

@@ -4116,7 +4116,9 @@
   {
     "name": "smooth-scrolling",
     "owners": [ "bokan", "input-dev" ],
-    "expiry_milestone": 85
+    // This needs to continue to be extended until the UI contains a proper
+    // option for it, see crbug.com/817814.
+    "expiry_milestone": 95
   },
   {
     "name": "sms-receiver-cross-device",