Bug 1422903 - Prevent about:privatebrowsing favicon from flickering. r=florian

We apply a custom workaround to show about:home and about:newtab favicons
as early as possible for perceived performance, but didn't previously consider
the about:privatebrowsing page (which can act as both about:home and about:newtab).

MozReview-Commit-ID: gPiV08h0j0

--HG--
extra : rebase_source : 12a6ed0973013ed68e783ca3d39a9492c5185411

browser/base/content/browser.js

@@ -1346,6 +1346,8 @@ var gBrowserInit = {
     this._uriToLoadPromise.then(uriToLoad => {
       if (uriToLoad == "about:home") {
         gBrowser.setIcon(gBrowser.selectedTab, "chrome://branding/content/icon32.png");
+      } else if (uriToLoad == "about:privatebrowsing") {
+        gBrowser.setIcon(gBrowser.selectedTab, "chrome://browser/skin/privatebrowsing/favicon.svg");
       }
     });
 

browser/base/content/tabbrowser.xml

@@ -801,7 +801,16 @@
 
                   // Ignore initial about:blank to prevent flickering.
                   if (!this.mBrowser.mIconURL && !ignoreBlank) {
-                    this.mTabBrowser.useDefaultIcon(this.mTab);
+                    // Don't switch to the default icon on about:home or about:newtab,
+                    // since these pages get their favicon set in browser code to
+                    // improve perceived performance.
+                    let isNewTab = originalLocation &&
+                      (originalLocation.spec == "about:newtab" ||
+                       originalLocation.spec == "about:privatebrowsing" ||
+                       originalLocation.spec == "about:home");
+                    if (!isNewTab) {
+                      this.mTabBrowser.useDefaultIcon(this.mTab);
+                    }
                   }
                 }
 
@@ -2813,8 +2822,10 @@
 
             // Hack to ensure that the about:newtab favicon is loaded
             // instantaneously, to avoid flickering and improve perceived performance.
-            if (aURI == BROWSER_NEW_TAB_URL) {
+            if (aURI == "about:newtab") {
               this.setIcon(t, "chrome://branding/content/icon32.png");
+            } else if (aURI == "about:privatebrowsing") {
+              this.setIcon(t, "chrome://browser/skin/privatebrowsing/favicon.svg");
             }
 
             // Dispatch a new tab notification.  We do this once we're

browser/components/privatebrowsing/content/aboutPrivateBrowsing.js

@@ -9,7 +9,6 @@ Cu.import("resource://gre/modules/PrivateBrowsingUtils.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 const FAVICON_QUESTION = "chrome://global/skin/icons/question-32.png";
-const FAVICON_PRIVACY = "chrome://browser/skin/privatebrowsing/favicon.svg";
 
 var stringBundle = Services.strings.createBundle(
                     "chrome://browser/locale/aboutPrivateBrowsing.properties");
@@ -38,10 +37,6 @@ var prefObserver = {
 prefBranch.addObserver("pbmode.enabled", prefObserver, true);
 prefBranch.addObserver("enabled", prefObserver, true);
 
-function setFavIcon(url) {
- document.getElementById("favicon").setAttribute("href", url);
-}
-
 document.addEventListener("DOMContentLoaded", function() {
  if (!PrivateBrowsingUtils.isContentWindowPrivate(window)) {
    document.documentElement.classList.remove("private");
@@ -60,8 +55,6 @@ document.addEventListener("DOMContentLoaded", function() {
  });
 
  document.title = stringBundle.GetStringFromName("title.head");
- document.getElementById("favicon")
-         .setAttribute("href", FAVICON_PRIVACY);
  tpToggle.addEventListener("change", toggleTrackingProtection);
  document.getElementById("startTour")
          .addEventListener("click", dontShowIntroPanelAgain);