Bug 705597 - about:blank subframe entries in session restore make browser slow; r=dietrich

browser/components/sessionstore/src/nsSessionStore.js

@@ -1861,6 +1861,8 @@ SessionStoreService.prototype = {
     var entry = { url: aEntry.URI.spec };
 
     try {
+      // throwing is expensive, we know that about: pages will throw
+      if (entry.url.indexOf("about:") != 0)
         aHostSchemeData.push({ host: aEntry.URI.host, scheme: aEntry.URI.scheme });
     }
     catch (ex) {
@@ -1959,24 +1961,26 @@ SessionStoreService.prototype = {
     }
     
     if (aEntry.childCount > 0) {
-      entry.children = [];
+      let children = [];
       for (var i = 0; i < aEntry.childCount; i++) {
         var child = aEntry.GetChildAt(i);
+
         if (child) {
-          entry.children.push(this._serializeHistoryEntry(child, aFullData,
-                                                          aIsPinned, aHostSchemeData));
-        }
-        else { // to maintain the correct frame order, insert a dummy entry 
-          entry.children.push({ url: "about:blank" });
-        }
           // don't try to restore framesets containing wyciwyg URLs (cf. bug 424689 and bug 450595)
-        if (/^wyciwyg:\/\//.test(entry.children[i].url)) {
-          delete entry.children;
+          if (child.URI.schemeIs("wyciwyg")) {
+            children = [];
             break;
           }
+
+          children.push(this._serializeHistoryEntry(child, aFullData,
+                                                    aIsPinned, aHostSchemeData));
         }
       }
 
+      if (children.length)
+        entry.children = children;
+    }
+    
     return entry;
   },
 

browser/components/sessionstore/test/browser/Makefile.in

@@ -159,6 +159,7 @@ _BROWSER_TEST_FILES = \
 	browser_687710.js \
 	browser_687710_2.js \
 	browser_694378.js \
+	browser_705597.js \
 	$(NULL)
 
 ifneq ($(OS_ARCH),Darwin)

browser/components/sessionstore/test/browser/browser_705597.js

@@ -0,0 +1,57 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+let tabState = {
+  entries: [{url: "about:home", children: [{url: "about:mozilla"}]}]
+};
+
+function test() {
+  waitForExplicitFinish();
+
+  let tab = gBrowser.addTab("about:blank");
+  registerCleanupFunction(function () gBrowser.removeTab(tab));
+
+  let browser = tab.linkedBrowser;
+
+  whenBrowserLoaded(browser, function () {
+    ss.setTabState(tab, JSON.stringify(tabState));
+
+    let sessionHistory = browser.sessionHistory;
+    let entry = sessionHistory.getEntryAtIndex(0, false);
+
+    whenChildCount(entry, 1, function () {
+      whenChildCount(entry, 2, function () {
+        whenBrowserLoaded(browser, function () {
+          let {entries} = JSON.parse(ss.getTabState(tab));
+          is(entries.length, 1, "tab has one history entry");
+          ok(!entries[0].children, "history entry has no subframes");
+
+          finish();
+        });
+
+        // reload the browser to deprecate the subframes
+        browser.reload();
+      });
+
+      // create a dynamic subframe
+      let doc = browser.contentDocument;
+      let iframe = doc.createElement("iframe");
+      iframe.setAttribute("src", "about:mozilla");
+      doc.body.appendChild(iframe);
+    });
+  });
+}
+
+function whenBrowserLoaded(aBrowser, aCallback) {
+  aBrowser.addEventListener("load", function onLoad() {
+    aBrowser.removeEventListener("load", onLoad, true);
+    executeSoon(aCallback);
+  }, true);
+}
+
+function whenChildCount(aEntry, aChildCount, aCallback) {
+  if (aEntry.childCount == aChildCount)
+    aCallback();
+  else
+    executeSoon(function () whenChildCount(aEntry, aChildCount, aCallback));
+}