Bug 1402256 - Add WebExtensions API to “warm up” a tab r=mixedpuppy

Differential Revision: https://phabricator.services.mozilla.com/D71873

browser/components/extensions/parent/ext-tabs.js

@@ -912,6 +912,12 @@ this.tabs = class extends ExtensionAPI {
           nativeTab.linkedBrowser.reloadWithFlags(flags);
         },
 
+        async warmup(tabId) {
+          let nativeTab = tabTracker.getTab(tabId);
+          let tabbrowser = nativeTab.ownerGlobal.gBrowser;
+          tabbrowser.warmupTab(nativeTab);
+        },
+
         async get(tabId) {
           return tabManager.get(tabId).convert();
         },

browser/components/extensions/schemas/tabs.json

@@ -1023,6 +1023,21 @@
           }
         ]
       },
+      {
+        "name": "warmup",
+        "type": "function",
+        "description": "Warm up a tab",
+        "async": "true",
+        "parameters": [
+          {
+            "type": "integer",
+            "name": "tabId",
+            "minimum": 0,
+            "optional": false,
+            "description": "The ID of the tab to warm up."
+          }
+        ]
+      },
       {
         "name": "remove",
         "type": "function",

browser/components/extensions/test/browser/browser.ini

@@ -270,6 +270,7 @@ skip-if = os == 'mac' # Save as PDF not supported on Mac OS X
 [browser_ext_tabs_update.js]
 [browser_ext_tabs_update_highlighted.js]
 [browser_ext_tabs_update_url.js]
+[browser_ext_tabs_warmup.js]
 [browser_ext_tabs_zoom.js]
 [browser_ext_themes_validation.js]
 [browser_ext_topSites.js]

browser/components/extensions/test/browser/browser_ext_tabs_warmup.js

@@ -0,0 +1,40 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+
+add_task(async function testWarmupTab() {
+  let tab1 = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    "http://example.net/"
+  );
+  let tab2 = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    "about:blank"
+  );
+  Assert.ok(!tab1.linkedBrowser.renderLayers, "tab is not warm yet");
+
+  let extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      permissions: ["tabs"],
+    },
+
+    background: async function() {
+      let backgroundTab = (
+        await browser.tabs.query({
+          lastFocusedWindow: true,
+          url: "http://example.net/",
+          active: false,
+        })
+      )[0];
+      await browser.tabs.warmup(backgroundTab.id);
+      browser.test.notifyPass("tabs.warmup");
+    },
+  });
+
+  await extension.startup();
+  await extension.awaitFinish("tabs.warmup");
+  Assert.ok(tab1.linkedBrowser.renderLayers, "tab has been warmed up");
+  gBrowser.removeTab(tab1);
+  gBrowser.removeTab(tab2);
+  await extension.unload();
+});