Enable PolicyRefreshRate on desktop.

I would guess this policy was marked Chrome OS only because at the
time Chrome OS was the only platfrom that had cloud management.
It technically works on all platfroms as it maps to a pref existing
on all platforms. The comment that when invalidation is available
and operation the policy is reset is also true and visible on
chrome://policy.

BUG=1011855
TEST=Existing tests already cover all code paths.

Change-Id: I3ebf105345ca71e0508a7170d6f829fae819354c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1864797Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Julian Pastarmov <pastarmovj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706915}

components/policy/resources/policy_templates.json

@@ -5815,7 +5815,7 @@
       'owners': ['file://components/policy/resources/OWNERS'],
       'type': 'int',
       'schema': { 'type': 'integer' },
-      'supported_on': ['chrome_os:11-'],
+      'supported_on': ['chrome_os:11-', 'chrome.*:79-'],
       'features': {
         'dynamic_refresh': True,
         'per_profile': True,