Extend chrome browser flag for WebP experiment.

Extends the decode-webp-images-to-yuv browser flag from M80 to M88.

Bug: 966008
Change-Id: Ic27dcf609abe1af58d380417c248f90958297737
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918944Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Sasha McIntosh <sashamcintosh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715852}

chrome/browser/flag-metadata.json

@@ -660,7 +660,7 @@
   {
     "name": "decode-webp-images-to-yuv",
     "owners": [ "andrescj", "chromeos-gfx@google.com" ],
-    "expiry_milestone": 80
+    "expiry_milestone": 88
   },
   {
     "name": "delegate-overscroll-swipes",