Show AlertDialog when WebAPKs are enabled in chrome://flags but Unknown sources is disabled

chrome/android/java/strings/android_chrome_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- android_chrome_strings.grd contains strings for Chrome for Android.
 
 FAQ:
   - How do I add, change, or remove a string?
       Just update this file.
   - Translations will happen automatically??
       Yes, indeed. Just add your string before the branch point and
       make the description good.
@@ skipping 2688 matching lines @@
       </message>
 
       <!-- Item Chooser UI strings -->
       <message name="IDS_ITEM_CHOOSER_ITEM_NAME_WITH_ID" desc="To distinguish items with the same name, the item chooser shows the item name with id.">
         <ph name="ITEM_NAME">%1$s<ex>item_name</ex></ph> (<ph name="ITEM_ID">%2$s<ex>item id</ex></ph>)
       </message>
 
       <message name="IDS_INSTANT_APPS_OPEN_IN_APP" desc="Button label for the user action that will open an Instant App.">
         Open app
       </message>
+
+      <!-- WebAPK related strings -->
+      <message name="IDS_WEBAPK_UNKNOWN_SOURCES_DIALOG_TITLE" desc="Title of dialog warning user that installation from Unknown sources is required for WebAPK experiment.">
+        Improved Add to Home screen Experiment
+      </message>
+
+      <message name="IDS_WEBAPK_UNKNOWN_SOURCES_DIALOG_MESSAGE_CANARY" desc="Text of dialog warning user that installation from Unknown sources is required for WebAPK experiment on Chrome Canary.">
+        Turn on “Unknown sources” in Android security settings to try "Improved Add to Home screen" experiment in Chrome Canary. Be sure to disable this setting when you’re done trying it out.
+      </message>
+
+      <message name="IDS_WEBAPK_UNKNOWN_SOURCES_DIALOG_MESSAGE_DEV" desc="Text of dialog warning user that installation from Unknown sources is required for WebAPK experiment on Chrome Dev.">
+        Turn on “Unknown sources” in Android security settings to try "Improved Add to Home screen" experiment in Chrome Dev. Be sure to disable this setting when you’re done trying it out.

[gone, 2016/11/07 18:27:13]

Not much value in differentiating between Canary in Dev in these strings.  Just
make it one string again.

[pkotwicz, 2016/11/07 20:08:13]

What are you suggesting changing the string to?

[gone, 2016/11/07 20:59:29]

Take out the "Dev"/"Canary" bits, which will collapse both into one string.

[gone, 2016/11/07 21:12:50]

I meant to keep Chrome, but to remove the channel.  lgtming this anyway because
the string still works.

+      </message>
+
+      <message name="IDS_WEBAPK_UNKNOWN_SOURCES_SETTINGS_BUTTON" desc="Button label for opening Android Settings from dialog warning user that installation from Unknown sources is required for WebAPK experiment.">
+        Settings
+      </message>
     </messages>
   </release>
 </grit>