Wait at least XXX ms before showing the loading content screen

Otherwise, the user just thinks the conversation is delayed for no
good reason.
May want to tweak number a bit, but its def better
hopefully, we can make this a bit smoother, too
gets janky when some parts of the webview/ header load before the conversation loads
May be able to add a scrim to block the visible jank, but the 3 layers in the conversation
view are making this a bit tricky
Fixes b/7133753 don't show loading progress view for conversation until XXX ms have passed

Change-Id: If141ff4c07de92ad3dadd15ff003d64d557a5ea4
diff --git a/res/values/constants.xml b/res/values/constants.xml
index c72125a..01e0f46 100644
--- a/res/values/constants.xml
+++ b/res/values/constants.xml
@@ -78,4 +78,7 @@
     <bool name="display_folder_colors_in_widget">false</bool>
 
     <integer name="max_num_notification_digest_items">10</integer>
+
+    <!-- Wait at least this long for the webview to render conversation content before showing the loading dialog -->
+    <integer name="conversationview_show_loading_delay">500</integer>
 </resources>