Bug 1148996 - Remove selected lightweight theme for mochitest and xpcshell tests;r=jmaher

This is for aurora (dev edition) compatibility.  In this channel, there is a
selected lightweight theme by default.  Tests don't expect this to be the case
so this simply resets the relevant prefs for mochitests and xpcshell tests.

testing/profiles/prefs_general.js

@@ -310,3 +310,8 @@ user_pref("browser.readinglist.introShown", true);
 // Don't let PAC generator to set PAC, as mochitest framework has its own PAC
 // rules during testing.
 user_pref("network.proxy.pac_generator", false);
+
+// Make tests run consistently on DevEdition (which has a lightweight theme
+// selected by default).
+user_pref("lightweightThemes.selectedThemeID", "");
+user_pref("browser.devedition.theme.enabled", false);

testing/xpcshell/head.js

@@ -1422,3 +1422,15 @@ try {
     prefs.setCharPref("browser.selfsupport.url", "https://%(server)s/selfsupport-dummy/");
   }
 } catch (e) { }
+
+// Make tests run consistently on DevEdition (which has a lightweight theme
+// selected by default).
+try {
+  if (runningInParent) {
+    let prefs = Components.classes["@mozilla.org/preferences-service;1"]
+      .getService(Components.interfaces.nsIPrefBranch);
+
+    prefs.deleteBranch("lightweightThemes.selectedThemeID");
+    prefs.deleteBranch("browser.devedition.theme.enabled");
+  }
+} catch (e) { }