Issue 1983 - Dispatch onLoading event for prerendered pages

chrome/ext/background.js

Index: chrome/ext/background.js
===================================================================
--- a/chrome/ext/background.js
+++ b/chrome/ext/background.js
@@ -102,10 +102,60 @@
     onLoading: new ext._EventTarget()
   };
 
-  chrome.tabs.onUpdated.addListener(function(tabId, changeInfo, tab)
+  chrome.webNavigation.onBeforeNavigate.addListener(function(details)
   {
-    if (changeInfo.status == "loading")
-      ext.pages.onLoading._dispatch(new Page(tab));
+    if (details.frameId == 0)
+    {
+      ext._removeFromAllPageMaps(details.tabId);
+
+      chrome.tabs.get(details.tabId, function()
+      {
+        if (chrome.runtime.lastError)
+        {
+          // If the tab is prerendered, chrome.tabs.get() sets
+          // chrome.runtime.lastError and we have to immediately dispatch the
+          // "onLoading" event, since "onUpdated" events aren't dispatched for
+          // prerendered tabs. The browserAction object (see above) then take
+          // care to delay changes until the tab becomes visible.
+          ext.pages.onLoading._dispatch(
+            new Page({
+              id: details.tabId,
+              url: details.url
+            })
+          );
+        }
+        else
+        {
+          // If the tab is already visible, we have to delay the "onLoading"
+          // event until the tab actually switches to "loading" status.
+          // Otherwise browser action changes get overridden when Chrome
+          // automatically resets them for the new page.
+          function onUpdated(tabId, changeInfo, tab)
+          {
+            if (tabId == details.tabId && changeInfo.status == "loading")
+            {
+              chrome.tabs.onUpdated.removeListener(onUpdated);
+              chrome.tabs.onRemoved.removeListener(onRemoved);
+
+              ext.pages.onLoading._dispatch(new Page(tab));
+            }
+          }
+          chrome.tabs.onUpdated.addListener(onUpdated);
+
+          // Make sure to not leak any callbacks, in case the tab
+          // is removed before its status changes to "loading".
+          function onRemoved(tabId)
+          {
+            if (tabId == details.tabId)
+            {
+              chrome.tabs.onUpdated.removeListener(onUpdated);
+              chrome.tabs.onRemoved.removeListener(onRemoved);
+            }
+          }
+          chrome.tabs.onRemoved.addListener(onRemoved);
+        }
+      });
+    }
   });
 
   function forgetTab(tabId)
@@ -114,12 +164,6 @@
     delete framesOfTabs[tabId];
   }
 
-  chrome.webNavigation.onBeforeNavigate.addListener(function(details)
-  {
-    if (details.frameId == 0)
-      forgetTab(details.tabId);
-  });
-
   chrome.tabs.onReplaced.addListener(function(addedTabId, removedTabId)
   {
     forgetTab(removedTabId);