Using postMessage so share UI can ask overlay to generate an data URL, since the web page cannot generate data URLs for images on other domains. Used for email message picture previews. Some JSLint nits too.

dev/play/designs/popup/index.js

@@ -53,21 +53,30 @@ function (require,   $,        fn,         rdapi,   oauth,   jig,         url,
     return text ? text.replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;') : text;
   }
 
+  function rawBase64(dataUrl) {
+    return dataUrl && dataUrl.replace("data:image/png;base64,", "");
+  }
+
   jig.addFn({
     thumb: function (options) {
-      if (!options.previews) { return ""; }
-      if (options.previews[0]["http_url"]) {
-        return escapeHtml(options.previews[0]["http_url"]);
+      var preview = options.previews && options.previews[0];
+      if (!preview) {
+        return "";
+      }
+      if (preview.http_url) {
+        return escapeHtml(preview.http_url);
       }
       // Return our data url, this is the thumbnail
-      return options.previews[0]["base64"];
+      return preview.base64;
     },
     preview: function (options) {
-      return options.previews && options.previews[0]["http_url"];
+      var preview = options.previews && options.previews[0];
+      return preview && preview.http_url;
     },
     preview_base64: function (options) {
       // Strip the URL down to just the base64 content
-      return options.previews && options.previews[0]["base64"].replace("data:image/png;base64,","");
+      var preview = options.previews && options.previews[0];
+      return preview && rawBase64(preview.base64);
     },
     link: function (options) {
       return options.canonicalUrl || options.url;
@@ -222,7 +231,7 @@ function (require,   $,        fn,         rdapi,   oauth,   jig,         url,
     var lastSelectionMatch = 0,
         accountsDom = $('#accounts'),
         fragment = document.createDocumentFragment(),
-        debugPanel,
+        debugPanel, preview,
         i = 0;
 
     if ((accounts && accounts.length)) {
@@ -259,6 +268,15 @@ function (require,   $,        fn,         rdapi,   oauth,   jig,         url,
         debugPanel = new DebugPanel({}, accountsDom[0]);
       }
 
+      //Ask extension to generate base64 data if none available.
+      //Useful for sending previews in email.
+      preview = options.previews && options.previews[0];
+      if (accounts.length && preview && preview.http_url && !preview.base64) {
+        dispatch.sub('base64Preview', function (dataUrl) {
+          $('[name="picture_base64"]').val(rawBase64(dataUrl));
+        });
+        dispatch.pub('generateBase64Preview', preview.http_url);
+      }
     } else {
       showStatus('statusSettings');
       return;