Change VizDisplayCompositor flag expiry.

Bump to M79 since we still need the flag.

Bug: none
Change-Id: Iaa06e3f8fd03dc9b52aa3c20ab5cba1dfe6097d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1762694
Auto-Submit: kylechar <kylechar@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688732}

chrome/browser/flag-metadata.json

@@ -1793,8 +1793,8 @@
   },
   {
     "name": "enable-viz-display-compositor",
-    "owners": [ "fsamuel", "kylechar" ],
-    "expiry_milestone": 76
+    "owners": [ "kylechar", "rjkroege" ],
+    "expiry_milestone": 79
   },
   {
     "name": "enable-viz-hit-test-surface-layer",