Bug 1357800 - The One-Off search buttons not visible in the search bar. r=florian

Rebuild the one-off search buttons when the theme changes.  See bug 1357800 for details.  Summary: On Linux, switching between themes can cause a row of buttons to disappear.

MozReview-Commit-ID: 8lfsUO00jYP

--HG--
extra : rebase_source : 5bdef5513a8c8f8f02fd9383867b0ed57610b606

browser/components/search/content/search.xml

@@ -1426,6 +1426,11 @@
         // Add weak referenced observers to invalidate our cached list of engines.
         Services.prefs.addObserver("browser.search.hiddenOneOffs", this, true);
         Services.obs.addObserver(this, "browser-search-engine-modified", true);
+
+        // Rebuild the buttons when the theme changes.  See bug 1357800 for
+        // details.  Summary: On Linux, switching between themes can cause a row
+        // of buttons to disappear.
+        Services.obs.addObserver(this, "lightweight-theme-changed", true);
       ]]></constructor>
 
       <!-- This handles events outside the one-off buttons, like on the popup