Bug 873749 - SideMenuWidget shouldn't automatically scroll to bottom when there's a selected item, r=rcampbell

browser/devtools/netmonitor/test/browser_net_autoscroll.js

@@ -21,7 +21,8 @@ function test() {
   // when the requests overflow the vertical size of the container.
   .then(() => {
     return waitForRequestsToOverflowContainer(monitor, requestsContainer);
-  }).then(() => {
+  })
+  .then(() => {
     ok(scrolledToBottom(requestsContainer), "Scrolled to bottom on overflow.");
   })
 
@@ -34,7 +35,8 @@ function test() {
     ok(!scrolledToBottom(requestsContainer), "Not scrolled to bottom.");
     scrollTop = requestsContainer.scrollTop; // save for comparison later
     return waitForNetworkEvents(monitor, 8);
-  }).then(() => {
+  })
+  .then(() => {
     is(requestsContainer.scrollTop, scrollTop, "Did not scroll.");
   })
 
@@ -44,10 +46,21 @@ function test() {
     requestsContainer.scrollTop = requestsContainer.scrollHeight;
     ok(scrolledToBottom(requestsContainer), "Set scroll position to bottom.");
     return waitForNetworkEvents(monitor, 8);
-  }).then(() => {
+  })
+  .then(() => {
     ok(scrolledToBottom(requestsContainer), "Still scrolled to bottom.");
   })
 
+  // (4) Now select an item in the list and check that additional requests
+  // do not change the scroll position.
+  .then(() => {
+    monitor.panelWin.NetMonitorView.RequestsMenu.selectedIndex = 0;
+    return waitForNetworkEvents(monitor, 8);
+  })
+  .then(() => {
+    is(requestsContainer.scrollTop, 0, "Did not scroll.");
+  })
+
   // Done; clean up.
   .then(() => {
     return teardown(monitor).then(finish);

browser/devtools/netmonitor/test/html_infinite-get-page.html

@@ -27,7 +27,7 @@
 
       (function performRequests() {
         get("request_" + (count++), function() {
-          setTimeout(performRequests, 0);
+          setTimeout(performRequests, 50);
         });
       })();
     </script>

browser/devtools/shared/widgets/SideMenuWidget.jsm

@@ -100,9 +100,17 @@ SideMenuWidget.prototype = {
     // Invalidate any notices set on this widget.
     this.removeAttribute("notice");
 
+    // Maintaining scroll position at the bottom when a new item is inserted
+    // depends on several factors (the order of testing is important to avoid
+    // needlessly expensive operations that may cause reflows):
     let maintainScrollAtBottom =
+      // 1. The behavior should be enabled,
       this.autoscrollWithAppendedItems &&
+      // 2. There shouldn't currently be any selected item in the list.
+      !this._selectedItem &&
+      // 3. The new item should be appended at the end of the list.
       (aIndex < 0 || aIndex >= this._orderedMenuElementsArray.length) &&
+      // 4. The list should already be scrolled at the bottom.
       (this._list.scrollTop + this._list.clientHeight >= this._list.scrollHeight);
 
     let group = this._getMenuGroupForName(aGroup);