Use real Help App resources for chromeOS devices.

Bug: 1012578, b/144121590
Change-Id: Ic66887aeb2eb7caa9ea1d464974ec11b350f6952
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1948386Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: Rachel Carpenter <carpenterr@google.com>
Cr-Commit-Position: refs/heads/master@{#721334}

chromeos/components/help_app_ui/help_app_ui.gni

@@ -3,5 +3,5 @@ import("//build/config/chrome_build.gni")
 declare_args() {
   # Whether to enable the "real" ChromeOS Help App. When false, a mock app is
   # bundled for testing integration points.
-  enable_cros_help_app = false
+  enable_cros_help_app = is_chromeos && is_chrome_branded
 }