waitForExplicitFinish(); let pageSource = '' + '

' + ''; let oldDiscardingPref, oldTab, newTab; let prefBranch = Cc["@mozilla.org/preferences-service;1"] .getService(Ci.nsIPrefService) .getBranch('image.mem.'); function ImageDiscardObserver(result) { this.discard = function onDiscard(request) { result.wasDiscarded = true; this.synchronous = false; } this.synchronous = true; } function currentRequest() { let img = gBrowser.getBrowserForTab(newTab).contentWindow .document.getElementById('testImg'); img.QueryInterface(Ci.nsIImageLoadingContent); return img.getRequest(Ci.nsIImageLoadingContent.CURRENT_REQUEST); } function attachDiscardObserver(result) { // Create the discard observer. let observer = new ImageDiscardObserver(result); let scriptedObserver = Cc["@mozilla.org/image/tools;1"] .getService(Ci.imgITools) .createScriptedObserver(observer); // Clone the current imgIRequest with our new observer. let request = currentRequest(); return request.clone(scriptedObserver); } function isImgDecoded() { let request = currentRequest(); return request.imageStatus & Ci.imgIRequest.STATUS_FRAME_COMPLETE ? true : false; } // Ensure that the image is decoded by drawing it to a canvas. function forceDecodeImg() { let doc = gBrowser.getBrowserForTab(newTab).contentWindow.document; let img = doc.getElementById('testImg'); let canvas = doc.createElement('canvas'); let ctx = canvas.getContext('2d'); ctx.drawImage(img, 0, 0); } function test() { // Enable the discarding pref. oldDiscardingPref = prefBranch.getBoolPref('discardable'); prefBranch.setBoolPref('discardable', true); // Create and focus a new tab. oldTab = gBrowser.selectedTab; newTab = gBrowser.addTab('data:text/html,' + pageSource); gBrowser.selectedTab = newTab; // Run step2 after the tab loads. gBrowser.getBrowserForTab(newTab) .addEventListener("pageshow", step2 ); } function step2() { // Attach a discard listener and create a place to hold the result. var result = { wasDiscarded: false }; var clonedRequest = attachDiscardObserver(result); // Check that the image is decoded. forceDecodeImg(); ok(isImgDecoded(), 'Image should initially be decoded.'); // Focus the old tab, then fire a memory-pressure notification. This should // cause the decoded image in the new tab to be discarded. gBrowser.selectedTab = oldTab; var os = Cc["@mozilla.org/observer-service;1"] .getService(Ci.nsIObserverService); os.notifyObservers(null, 'memory-pressure', 'heap-minimize'); ok(result.wasDiscarded, 'Image should be discarded.'); // And we're done. gBrowser.removeTab(newTab); prefBranch.setBoolPref('discardable', oldDiscardingPref); clonedRequest.cancelAndForgetObserver(0); finish(); }