[script] Update build_all_plugins_app to exclude some plugins in `master`. (#3432)

diff --git a/script/build_all_plugins_app.sh b/script/build_all_plugins_app.sh
index ca97c05..72390c2 100755
--- a/script/build_all_plugins_app.sh
+++ b/script/build_all_plugins_app.sh
@@ -56,6 +56,10 @@
 if [ "$CHANNEL" == "stable" ]; then
   ALL_EXCLUDED=("$EXCLUDED,$EXCLUDED_PLUGINS_FROM_STABLE")
 fi
+# Exclude non-nnbd plugins from master.
+if [ "$CHANNEL" != "stable" ]; then
+  ALL_EXCLUDED=("$EXCLUDED,$EXCLUDED_PLUGINS_FROM_MASTER")
+fi
 
 echo "Excluding the following plugins: $ALL_EXCLUDED"
 
diff --git a/script/nnbd_plugins.sh b/script/nnbd_plugins.sh
index 7bc5ac3..b2ca25b 100644
--- a/script/nnbd_plugins.sh
+++ b/script/nnbd_plugins.sh
@@ -21,4 +21,22 @@
   "webview_flutter"
 )
 
+# This list contains the list of plugins that have *not* been
+# migrated to nnbd, and conflict with those that have when
+# building the all plugins app. This list should be kept empty.
+
+readonly NON_NNBD_PLUGINS_LIST=(
+  # "android_alarm_manager"
+  "camera"
+  # "file_selector"
+  # "google_maps_flutter"
+  # "image_picker"
+  # "in_app_purchase"
+  # "quick_actions"
+  # "sensors"
+  # "shared_preferences"
+  # "wifi_info_flutter"
+)
+
 export EXCLUDED_PLUGINS_FROM_STABLE=$(IFS=, ; echo "${NNBD_PLUGINS_LIST[*]}")
+export EXCLUDED_PLUGINS_FROM_MASTER=$(IFS=, ; echo "${NON_NNBD_PLUGINS_LIST[*]}")