Change chrome://flags to say "Restart Now" if on ChromeOS.

This is the expected behaviour (there was a typo in flags page template)

Change-Id: I94a318b03df8bd133d49e2d8d4b345770cd6e864
Reviewed-on: https://chromium-review.googlesource.com/1105654Reviewed-by: calamity <calamity@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568369}

components/flags_ui/resources/flags.html

@@ -205,10 +205,10 @@
         <div class="flex">
 <if expr="not is_ios">
           <button class="experiment-restart-button" type="button" tabindex="9">
-<if expr="not is_chromeos">
+<if expr="not chromeos">
           Relaunch Now
 </if>
-<if expr="is_chromeos">
+<if expr="chromeos">
           Restart Now
 </if>
           </button>