Update product type mapping

Android Appliance reuses the Android Things product
type instead of falling through to Android TV.

Bug: b/171569831
Test: local product build/manual test
Change-Id: I4161ba6555bb4471677a0a6da4c9eb3129c7f285
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2496193
Auto-Submit: Brett Kilty <brettk@google.com>
Commit-Queue: Luke Halliwell (slow) <halliwell@chromium.org>
Reviewed-by: Luke Halliwell (slow) <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821776}

chromecast/base/BUILD.gn

@@ -16,7 +16,8 @@ declare_args() {
   if (is_android_arc) {
     cast_product_type = 7  # CAST_PRODUCT_TYPE_CHROME_OS
   } else if (is_android) {
-    if (is_android_things) {
+    if (is_android_appliance) {
+      # Android Things and Appliances under the Android Things product type.
       cast_product_type = 6  # CAST_PRODUCT_TYPE_ANDROID_THINGS
     } else {
       cast_product_type = 4  # CAST_PRODUCT_TYPE_ANDROID_TV