vk: Add cloud handwriting service to extension whitelist.

Change-Id: I51f0c14c738ba2a6592ddd8ae73726fe2802d926
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2035816
Commit-Queue: dstockwell <dstockwell@chromium.org>
Auto-Submit: Darren Shen <shend@chromium.org>
Reviewed-by: dstockwell <dstockwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738411}

chrome/browser/resources/chromeos/input_method/google_xkb_manifest.json

@@ -13,6 +13,7 @@
     "audioCapture",
     "https://clients4.google.com/",
     "https://dl.google.com/",
+    "https://handwriting.googleapis.com/",
     "https://www.googleapis.com/",
     "input",
     "inputMethodPrivate",