Fix inconsistent spacing and trailing commas in objects in extensions/ files, so we can enable the comma-dangle and object-curly-spacing ESLint rules later on

http://eslint.org/docs/rules/comma-dangle
http://eslint.org/docs/rules/object-curly-spacing

Given that we currently have quite inconsistent object formatting, fixing this in in one big patch probably wouldn't be feasible (since I cannot imagine anyone wanting to review that); hence I've opted to try and do this piecewise instead.

Please note: This patch was created automatically, using the ESLint `--fix` command line option. In a couple of places this caused lines to become too long, and I've fixed those manually; please refer to the interdiff below for the only hand-edits in this patch.

```diff
diff --git a/extensions/firefox/content/PdfStreamConverter.jsm b/extensions/firefox/content/PdfStreamConverter.jsm
index ea91a71a..0d59dad1 100644
--- a/extensions/firefox/content/PdfStreamConverter.jsm
+++ b/extensions/firefox/content/PdfStreamConverter.jsm
@@ -773,7 +773,8 @@ class RequestListener {
         response = function sendResponse(aResponse) {
           try {
             var listener = doc.createEvent("CustomEvent");
-            let detail = Cu.cloneInto({ response: aResponse, }, doc.defaultView);
+            let detail = Cu.cloneInto({ response: aResponse, },
+                                      doc.defaultView);
             listener.initCustomEvent("pdf.js.response", true, false, detail);
             return message.dispatchEvent(listener);
           } catch (e) {
```

extensions/chromium/contentscript.js

@@ -103,7 +103,7 @@ function watchObjectOrEmbed(elem) {
     attributes: true,
     childList: false,
     characterData: false,
-    attributeFilter: [srcAttribute]
+    attributeFilter: [srcAttribute],
   });
 }