Bug 740581 - Make about:home's Sync button label not directly use the brand string.

r=fryn

browser/base/content/abouthome/aboutHome.xhtml

@@ -97,7 +97,7 @@
       <button class="launchButton" id="history">&abouthome.historyButton.label;</button>
       <button class="launchButton" id="apps" hidden="true">&abouthome.appsButton.label;</button>
       <button class="launchButton" id="addons">&abouthome.addonsButton.label;</button>
-      <button class="launchButton" id="sync">&syncBrand.shortName.label;</button>
+      <button class="launchButton" id="sync">&abouthome.syncButton.label;</button>
       <button class="launchButton" id="settings">&abouthome.settingsButton.label;</button>
       <div id="restorePreviousSessionSeparator"/>
       <button class="launchButton" id="restorePreviousSession">&historyRestoreLastSession.label;</button>

browser/locales/en-US/chrome/browser/aboutHome.dtd

@@ -24,3 +24,4 @@
 <!ENTITY abouthome.addonsButton.label    "Add-ons">
 <!ENTITY abouthome.appsButton.label      "Marketplace">
 <!ENTITY abouthome.downloadsButton.label "Downloads">
+<!ENTITY abouthome.syncButton.label      "&syncBrand.shortName.label;">