Bug 1299053 - Ensure that background pages have windowId -1 in browser.extension.getViews r=aswan

MozReview-Commit-ID: HdayD0JrIBm

--HG--
extra : rebase_source : 5dbf78b9f735cd086e800806b2ad76669dbd67f5

browser/components/extensions/test/browser/browser_ext_getViews.js

@@ -131,6 +131,7 @@ add_task(async function() {
   }
 
   await checkViews("background", 0, 0, 0);
+  await checkViewsWithFilter({windowId: -1}, 1);
   await checkViewsWithFilter({tabId: -1}, 1);
 
   let tabId1 = await openTab(winId1);

toolkit/components/extensions/ExtensionPageChild.jsm

@@ -153,6 +153,7 @@ class ExtensionBaseContextChild extends BaseContext {
       let globalView = ExtensionPageChild.contentGlobals.get(this.messageManager);
       return globalView ? globalView.windowId : -1;
     }
+    return -1;
   }
 
   get tabId() {