Bug 1192720 - prevent re-entrancy in event handling in tabbrowser.xml's _switcher, r=billm

--HG--
extra : commitid : AZ2VdDPujAp
extra : rebase_source : 753ec1a07ea81fc35992065d67eaa1fedd93bbf7
extra : amend_source : d63d242d9f013f7aa5706b6b63d45d01d6390a07

browser/base/content/tabbrowser.xml

@@ -3086,6 +3086,9 @@
             STATE_LOADED: 2,
             STATE_UNLOADING: 3,
 
+            // re-entrancy guard:
+            _processing: false,
+
             getTabState: function(tab) {
               let state = this.tabState.get(tab);
               if (state === undefined) {
@@ -3228,7 +3231,6 @@
               }
 
               this.lastVisibleTab = this.visibleTab;
-
             },
 
             assert: function(cond) {
@@ -3441,7 +3443,17 @@
               this.postActions();
             },
 
-            handleEvent: function(event) {
+            handleEvent: function(event, delayed = false) {
+              if (this._processing) {
+                setTimeout(() => this.handleEvent(event, true), 0);
+                return;
+              }
+              if (delayed && this.tabbrowser._switcher != this) {
+                // if we delayed processing this event, we might be out of date, in which
+                // case we drop the delayed events
+                return;
+              }
+              this._processing = true;
               this.preActions();
 
               if (event.type == "MozLayerTreeReady") {
@@ -3455,6 +3467,7 @@
               }
 
               this.postActions();
+              this._processing = false;
             },
 
             /*