Update expiration of PaintHolding flag to M-82

Bug: 1012732
Change-Id: I08a80067e26ba62593f46a6d7e4c89efae1b5910
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918098
Auto-Submit: Stephen Chenney <schenney@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715792}

chrome/browser/flag-metadata.json

@@ -1625,7 +1625,7 @@
     {
     "name": "enable-paint-holding",
     "owners": [ "schenney", "paint-dev" ],
-    "expiry_milestone": 80
+    "expiry_milestone": 82
   },
   {
     "name": "enable-parallel-downloading",