Bug 1169993 - Fix setTheme in theme.js to really trigger a theme change in Developer Tools. r=bgrins

browser/devtools/shared/test/browser_theme.js

@@ -27,6 +27,14 @@ function testGetTheme () {
 
 function testSetTheme () {
   let originalTheme = getTheme();
+  gDevTools.once("pref-changed", (_, { pref, oldValue, newValue }) => {
+    is(pref, "devtools.theme",
+      "The 'pref-changed' event triggered by setTheme has correct pref.");
+    is(oldValue, originalTheme,
+      "The 'pref-changed' event triggered by setTheme has correct oldValue.");
+    is(newValue, "dark",
+      "The 'pref-changed' event triggered by setTheme has correct newValue.");
+  });
   setTheme("dark");
   is(Services.prefs.getCharPref("devtools.theme"), "dark", "setTheme() correctly sets dark theme.");
   setTheme("light");

browser/devtools/shared/theme.js

@@ -85,10 +85,12 @@ const getColor = exports.getColor = (type, theme) => {
  * the themeing.
  */
 const setTheme = exports.setTheme = (newTheme) => {
+  let oldTheme = getTheme();
+
   Services.prefs.setCharPref("devtools.theme", newTheme);
   gDevTools.emit("pref-changed", {
     pref: "devtools.theme",
     newValue: newTheme,
-    oldValue: getTheme()
+    oldValue: oldTheme
   });
 };