flags: Extend show-overdraw-feedback till M88.

This CL renews the "show-overdraw-feedback" until M88. The flag will
likely become obsolete once SkiaRenderer is launched in all platforms, so
no need to mark it as never-expire.

Bug: None.
Test: None.
Change-Id: I4398ec4bb8f941529218a93947c99f7f52dd938d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2367450Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Commit-Queue: Andres Calderon Jaramillo <andrescj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800335}

chrome/browser/flag-metadata.json

@@ -4090,7 +4090,7 @@
   {
     "name": "show-overdraw-feedback",
     "owners": [ "andrescj", "chromeos-gfx@google.com" ],
-    "expiry_milestone": 85
+    "expiry_milestone": 88
   },
   {
     "name": "show-taps",