Make all the polymer elements CSP compliant.

elements/viewer-button/viewer-button.html

-<polymer-element name="viewer-button" attributes="src latchable">
+<polymer-element name="viewer-button" attributes="img latchable">
 <template>
   <link rel="stylesheet" href="viewer-button.css">
   <div id="icon"></div>
 </template>
-<script>
-  (function() {
-    var dpi = '';
-
-    Polymer('viewer-button', {
-      src: '',
-      latchable: false,
-      ready: function() {
-        if (!dpi) {
-          var mql = window.matchMedia('(-webkit-min-device-pixel-ratio: 1.3');
-          dpi = mql.matches ? 'hi' : 'low';
-        }
-      },
-      srcChanged: function() {
-        if (this.src) {
-          this.$.icon.style.backgroundImage =
-              'url(' + this.getAttribute('assetpath') + 'img/' + dpi +
-              'DPI/' + this.src + ')';
-        } else {
-          this.$.icon.style.backgroundImage = '';
-        }
-      },
-      latchableChanged: function() {
-        if (this.latchable)
-          this.classList.add('latchable');
-        else
-          this.classList.remove('latchable');
-      },
-    });
-  })();
-</script>
+<script src="viewer-button.js"></script>
 </polymer-element>