Bug 1590239 - Send a "browsing-context-discarded" notification when detaching, r=nika

Differential Revision: https://phabricator.services.mozilla.com/D50520

--HG--
extra : moz-landing-system : lando

docshell/base/BrowsingContext.cpp

@@ -29,11 +29,13 @@
 #include "mozilla/Components.h"
 #include "mozilla/HashTable.h"
 #include "mozilla/Logging.h"
+#include "mozilla/Services.h"
 #include "mozilla/StaticPtr.h"
 #include "nsIURIFixup.h"
 
 #include "nsDocShell.h"
 #include "nsGlobalWindowOuter.h"
+#include "nsIObserverService.h"
 #include "nsContentUtils.h"
 #include "nsScriptError.h"
 #include "nsThreadUtils.h"
@@ -362,6 +364,12 @@ void BrowsingContext::Detach(bool aFromIPC) {
   mGroup->Unregister(this);
   mIsDiscarded = true;
 
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  if (obs) {
+    obs->NotifyObservers(ToSupports(this), "browsing-context-discarded",
+                         nullptr);
+  }
+
   // NOTE: Doesn't use SetClosed, as it will be set in all processes
   // automatically by calls to Detach()
   mClosed = true;

docshell/test/browser/browser.ini

@@ -145,3 +145,4 @@ support-files =
 [browser_cross_process_csp_inheritance.js]
 skip-if = !e10s # e10s specific test.
 [browser_tab_replace_while_loading.js]
+[browser_browsing_context_discarded.js]

docshell/test/browser/browser_browsing_context_discarded.js

@@ -0,0 +1,36 @@
+"use strict";
+
+const TOPIC = "browsing-context-discarded";
+
+add_task(async function toplevel() {
+  let win = await BrowserTestUtils.openNewBrowserWindow();
+  let bc = await SpecialPowers.spawn(
+    win.gBrowser.selectedBrowser,
+    [],
+    () => content.docShell.browsingContext
+  );
+
+  let promise = BrowserUtils.promiseObserved(TOPIC, subject => subject === bc);
+  await BrowserTestUtils.closeWindow(win);
+  await promise;
+
+  // If we make it here, then we've received the notification.
+  ok(true, "got top-level notification");
+});
+
+add_task(async function subframe() {
+  let win = await BrowserTestUtils.openNewBrowserWindow();
+  let bc = await SpecialPowers.spawn(win.gBrowser.selectedBrowser, [], () => {
+    let iframe = content.document.createElement("iframe");
+    content.document.body.appendChild(iframe);
+    iframe.contentWindow.location = "https://example.com/";
+    return iframe.browsingContext;
+  });
+
+  let promise = BrowserUtils.promiseObserved(TOPIC, subject => subject === bc);
+  await BrowserTestUtils.closeWindow(win);
+  await promise;
+
+  // If we make it here, then we've received the notification.
+  ok(true, "got subframe notification");
+});