Bug 1387890 - Pass parentId for tabs opened by webextensions on Android. r=kmag

... so that pressing the back button eventually closes that tab and returns to the previous tab instead of simply backgrounding Firefox.

MozReview-Commit-ID: DuaA3anCsvn

--HG--
extra : rebase_source : 1c47a137730cbc3ebf0d2ba12f9947611922021c

mobile/android/components/extensions/ext-tabs.js

@@ -270,6 +270,8 @@ this.tabs = class extends ExtensionAPI {
           // and instead always get a NullPrincipal.
           options.disallowInheritPrincipal = true;
 
+          options.parentId = BrowserApp.selectedTab.id;
+
           tabListener.initTabReady();
           let nativeTab = BrowserApp.addTab(url, options);