[Spellcheck] Extend Windows native spell check flags

Windows native spell checker integration in Chromium is still under
development and the two associated feature flags must be extended.

Bug: 978460
Change-Id: I10b252b84fd728b79f73f32e568c644830e3573f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2163154Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Commit-Queue: Guillaume Jenkins <gujen@google.com>
Cr-Commit-Position: refs/heads/master@{#762094}

chrome/browser/flag-metadata.json

@@ -4240,12 +4240,12 @@
   {
     "name": "win-use-hybrid-spellchecker",
     "owners": [ "gujen@google.com", "chrome-language@google.com" ],
-    "expiry_milestone": 83
+    "expiry_milestone": 88
   },
   {
     "name": "win-use-native-spellchecker",
     "owners": [ "gujen@google.com", "chrome-language@google.com" ],
-    "expiry_milestone": 83
+    "expiry_milestone": 88
   },
   {
     "name": "zero-copy-video-capture",