Bug 1423220 - Don't delay activating the DocShell for tabs that we're rendering by switching and not warming. r=dthayer

MozReview-Commit-ID: 3UmocajaSWJ

--HG--
extra : rebase_source : f79b07bd5620312b959503aeee5410c2e205a471

browser/modules/AsyncTabSwitcher.jsm

@@ -254,7 +254,9 @@ class AsyncTabSwitcher {
     if (state == this.STATE_LOADING) {
       this.assert(!this.minimizedOrFullyOccluded);
 
-      if (!this.tabbrowser.tabWarmingEnabled) {
+      // If we're not in the process of warming this tab, we
+      // don't need to delay activating its DocShell.
+      if (!this.warmingTabs.has(tab)) {
         browser.docShellIsActive = true;
       }