1 files changed, 117 insertions, 0 deletions
diff --git a/gfx/layers/apz/test/mochitest/browser_test_background_tab_load_scroll.js b/gfx/layers/apz/test/mochitest/browser_test_background_tab_load_scroll.js
new file mode 100644
index 0000000000..9878907603
--- /dev/null
+++ b/gfx/layers/apz/test/mochitest/browser_test_background_tab_load_scroll.js
@@ -0,0 +1,117 @@
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/gfx/layers/apz/test/mochitest/apz_test_utils.js",
+  this
+);
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/gfx/layers/apz/test/mochitest/apz_test_native_event_utils.js",
+  this
+);
+
+add_task(async function test_main() {
+  // Open a specific page in a background tab, then switch to the tab, check if
+  // the visual and layout scroll offsets have diverged.
+  // Then change to another tab so it's background again. Then reload it. Then
+  // change back to it and check again if the visual and layout scroll offsets
+  // have diverged.
+  // The page has a couple important properties to trigger the bug. We need to
+  // be restoring a non-zero scroll position so that we call ScrollToImpl with
+  // origin restore so that we do not set the visual viewport offset. We then
+  // need to call ScrollToImpl with a origin that does not get clobber by apz
+  // so that we (wrongly) set the visual viewport offset.
+
+  requestLongerTimeout(2);
+
+  async function twoRafsInContent(browser) {
+    await SpecialPowers.spawn(browser, [], async function () {
+      await new Promise(r =>
+        content.requestAnimationFrame(() => content.requestAnimationFrame(r))
+      );
+    });
+  }
+
+  async function waitForApzInContent(browser) {
+    await SpecialPowers.spawn(browser, [], async () => {
+      await content.wrappedJSObject.waitUntilApzStable();
+      await content.wrappedJSObject.promiseApzFlushedRepaints();
+    });
+  }
+
+  async function checkScrollPosInContent(browser, iter, num) {
+    let visualScrollPos = await SpecialPowers.spawn(browser, [], function () {
+      const offsetX = {};
+      const offsetY = {};
+      SpecialPowers.getDOMWindowUtils(content).getVisualViewportOffset(
+        offsetX,
+        offsetY
+      );
+      return offsetY.value;
+    });
+
+    let scrollPos = await SpecialPowers.spawn(browser, [], function () {
+      return content.window.scrollY;
+    });
+
+    // When this fails the difference is at least 10000.
+    ok(
+      Math.abs(scrollPos - visualScrollPos) < 2,
+      "expect scroll position and visual scroll position to be the same: visual " +
+        visualScrollPos +
+        " scroll " +
+        scrollPos +
+        " (" +
+        iter +
+        "," +
+        num +
+        ")"
+    );
+  }
+
+  for (let i = 0; i < 5; i++) {
+    let blankurl = "about:blank";
+    let blankTab = BrowserTestUtils.addTab(gBrowser, blankurl);
+    let blankbrowser = blankTab.linkedBrowser;
+    await BrowserTestUtils.browserLoaded(blankbrowser, false, blankurl);
+
+    let url =
+      "http://mochi.test:8888/browser/gfx/layers/apz/test/mochitest/helper_background_tab_load_scroll.html";
+    let backgroundTab = BrowserTestUtils.addTab(gBrowser, url);
+    let browser = backgroundTab.linkedBrowser;
+    await BrowserTestUtils.browserLoaded(browser, false, url);
+    dump("Done loading background tab\n");
+
+    await twoRafsInContent(browser);
+
+    // Switch to the foreground.
+    await BrowserTestUtils.switchTab(gBrowser, backgroundTab);
+    dump("Switched background tab to foreground\n");
+
+    await waitForApzInContent(browser);
+
+    await checkScrollPosInContent(browser, i, 1);
+
+    await BrowserTestUtils.switchTab(gBrowser, blankTab);
+
+    browser.reload();
+    await BrowserTestUtils.browserLoaded(browser, false, url);
+
+    await twoRafsInContent(browser);
+
+    // Switch to the foreground.
+    await BrowserTestUtils.switchTab(gBrowser, backgroundTab);
+    dump("Switched background tab to foreground\n");
+
+    await waitForApzInContent(browser);
+
+    await checkScrollPosInContent(browser, i, 2);
+
+    // Cleanup
+    let tabClosed = BrowserTestUtils.waitForTabClosing(backgroundTab);
+    BrowserTestUtils.removeTab(backgroundTab);
+    await tabClosed;
+
+    let blanktabClosed = BrowserTestUtils.waitForTabClosing(blankTab);
+    BrowserTestUtils.removeTab(blankTab);
+    await blanktabClosed;
+  }
+});