Bug 1091901: fix tracking protection UI icon for hidpi, r=gijs

--HG--
extra : rebase_source : d8c1e94fa80a3bed1f9ecb0edb93166b04dc2112

browser/components/preferences/in-content/privacy.xul

@@ -80,7 +80,7 @@
                 preference="privacy.trackingprotection.enabled"
                 accesskey="&trackingProtection.accesskey;"
                 label="&trackingProtection.label;" />
-      <image id="trackingProtectionImage" src="chrome://browser/skin/bad-content-blocked-16.png"/>
+      <image id="trackingProtectionImage"/>
     </hbox>
     <label id="trackingProtectionLearnMore"
            class="text-link"

browser/themes/shared/incontentprefs/preferences.css

@@ -295,6 +295,18 @@ description > html|a {
   -moz-margin-start: 33px;
 }
 
+#trackingProtectionImage {
+  width: 16px;
+  height: 16px;
+  list-style-image: url(chrome://browser/skin/bad-content-blocked-16.png);
+}
+
+@media (min-resolution: 2dppx) {
+  #trackingProtectionImage {
+    list-style-image: url(chrome://browser/skin/bad-content-blocked-16@2x.png);
+  }
+}
+
 /**
  * Sub-dialog
  */