Bug 1395525 - Make all changes landed as part of tracker request tailing preferrable. r=dragana

dom/base/nsContentUtils.cpp

@@ -304,6 +304,7 @@ bool nsContentUtils::sGetBoxQuadsEnabled = false;
 bool nsContentUtils::sSkipCursorMoveForSameValueSet = false;
 bool nsContentUtils::sRequestIdleCallbackEnabled = false;
 bool nsContentUtils::sLowerNetworkPriority = false;
+bool nsContentUtils::sTailingEnabled = false;
 bool nsContentUtils::sShowInputPlaceholderOnFocus = true;
 bool nsContentUtils::sAutoFocusEnabled = true;
 #ifndef RELEASE_OR_BETA
@@ -768,6 +769,9 @@ nsContentUtils::Init()
   Preferences::AddBoolVarCache(&sLowerNetworkPriority,
                                "privacy.trackingprotection.lower_network_priority", false);
 
+  Preferences::AddBoolVarCache(&sTailingEnabled,
+                               "network.http.tailing.enabled", true);
+
   Preferences::AddBoolVarCache(&sShowInputPlaceholderOnFocus,
                                "dom.placeholder.show_on_focus", true);
 

dom/base/nsContentUtils.h

@@ -3093,6 +3093,9 @@ public:
   // if we want to lower the priority of the channel.
   static bool IsLowerNetworkPriority() { return sLowerNetworkPriority; }
 
+  // Whether tracker tailing is turned on - "network.http.tailing.enabled".
+  static bool IsTailingEnabled() { return sTailingEnabled; }
+
   // Check pref "dom.placeholder.show_on_focus" to see
   // if we want to show the placeholder inside input elements
   // when they have focus.
@@ -3284,6 +3287,7 @@ private:
   static bool sSkipCursorMoveForSameValueSet;
   static bool sRequestIdleCallbackEnabled;
   static bool sLowerNetworkPriority;
+  static bool sTailingEnabled;
   static bool sShowInputPlaceholderOnFocus;
   static bool sAutoFocusEnabled;
 #ifndef RELEASE_OR_BETA

dom/fetch/FetchDriver.cpp

@@ -378,10 +378,12 @@ FetchDriver::HttpFetch()
     }
   }
 
-  if (mIsTrackingFetch && nsContentUtils::IsLowerNetworkPriority()) {
+  if (mIsTrackingFetch && nsContentUtils::IsTailingEnabled()) {
     cos->AddClassFlags(nsIClassOfService::Throttleable |
                        nsIClassOfService::Tail);
+  }
 
+  if (mIsTrackingFetch && nsContentUtils::IsLowerNetworkPriority()) {
     nsCOMPtr<nsISupportsPriority> p = do_QueryInterface(chan);
     if (p) {
       p->SetPriority(nsISupportsPriority::PRIORITY_LOWEST);

dom/script/ScriptLoader.cpp

@@ -1067,7 +1067,12 @@ ScriptLoader::StartLoad(ScriptLoadRequest* aRequest)
       // synchronous head scripts block loading of most other non js/css
       // content such as images, Leader implicitely disallows tailing
       cos->AddClassFlags(nsIClassOfService::Leader);
-    } else if (defer && !async) {
+    } else if (defer && (!async || !nsContentUtils::IsTailingEnabled())) {
+      // Bug 1395525 and the !nsContentUtils::IsTailingEnabled() bit:
+      // We want to make sure that turing tailing off by the pref makes
+      // the browser behave exactly the same way as before landing
+      // the tailing patch, which has added the "&& !async" part.
+
       // head/body deferred scripts are blocked by leaders but are not
       // allowed tailing because they block DOMContentLoaded
       cos->AddClassFlags(nsIClassOfService::TailForbidden);

dom/xhr/XMLHttpRequestMainThread.cpp

@@ -2621,13 +2621,15 @@ XMLHttpRequestMainThread::MaybeLowerChannelPriority()
     return;
   }
 
-  nsCOMPtr<nsIClassOfService> cos = do_QueryInterface(mChannel);
-  if (cos) {
-    // Adding TailAllowed to overrule the Unblocked flag, but to preserve
-    // the effect of Unblocked when tailing is off.
-    cos->AddClassFlags(nsIClassOfService::Throttleable |
-                       nsIClassOfService::Tail |
-                       nsIClassOfService::TailAllowed);
+  if (nsContentUtils::IsTailingEnabled()) {
+    nsCOMPtr<nsIClassOfService> cos = do_QueryInterface(mChannel);
+    if (cos) {
+      // Adding TailAllowed to overrule the Unblocked flag, but to preserve
+      // the effect of Unblocked when tailing is off.
+      cos->AddClassFlags(nsIClassOfService::Throttleable |
+                         nsIClassOfService::Tail |
+                         nsIClassOfService::TailAllowed);
+    }
   }
 
   nsCOMPtr<nsISupportsPriority> p = do_QueryInterface(mChannel);

netwerk/base/nsChannelClassifier.cpp

@@ -210,16 +210,23 @@ LowerPriorityHelper(nsIChannel* aChannel)
 
   nsCOMPtr<nsIClassOfService> cos(do_QueryInterface(aChannel));
   if (cos) {
-    uint32_t cosFlags = 0;
-    cos->GetClassFlags(&cosFlags);
-    isBlockingResource = cosFlags & (nsIClassOfService::UrgentStart |
-                                     nsIClassOfService::Leader |
-                                     nsIClassOfService::Unblocked);
+    if (nsContentUtils::IsTailingEnabled()) {
+      uint32_t cosFlags = 0;
+      cos->GetClassFlags(&cosFlags);
+      isBlockingResource = cosFlags & (nsIClassOfService::UrgentStart |
+                                       nsIClassOfService::Leader |
+                                       nsIClassOfService::Unblocked);
+
+      // Requests not allowed to be tailed are usually those with higher
+      // prioritization.  That overweights being a tracker: don't throttle
+      // them when not in background.
+      if (!(cosFlags & nsIClassOfService::TailForbidden)) {
+        cos->AddClassFlags(nsIClassOfService::Throttleable);
+      }
+    } else {
+      // Yes, we even don't want to evaluate the isBlockingResource when tailing is off
+      // see bug 1395525.
 
-    // Requests not allowed to be tailed are usually those with higher
-    // prioritization.  That overweights being a tracker: don't throttle
-    // them when not in background.
-    if (!(cosFlags & nsIClassOfService::TailForbidden)) {
       cos->AddClassFlags(nsIClassOfService::Throttleable);
     }
   }

netwerk/protocol/http/nsHttpChannel.cpp

@@ -7576,7 +7576,6 @@ nsHttpChannel::OnStopRequest(nsIRequest *request, nsISupports *ctxt, nsresult st
                    "We should not call OnStopRequest twice");
         mListener->OnStopRequest(this, mListenerContext, status);
         mOnStopRequestCalled = true;
-
     }
 
     RemoveAsNonTailRequest();

toolkit/components/places/FaviconHelpers.cpp

@@ -594,10 +594,12 @@ AsyncFetchAndSetIconForPage::FetchFromNetwork() {
     priorityChannel->AdjustPriority(nsISupportsPriority::PRIORITY_LOWEST);
   }
 
-  nsCOMPtr<nsIClassOfService> cos = do_QueryInterface(channel);
-  if (cos) {
-    cos->AddClassFlags(nsIClassOfService::Tail |
-                       nsIClassOfService::Throttleable);
+  if (nsContentUtils::IsTailingEnabled()) {
+    nsCOMPtr<nsIClassOfService> cos = do_QueryInterface(channel);
+    if (cos) {
+      cos->AddClassFlags(nsIClassOfService::Tail |
+                         nsIClassOfService::Throttleable);
+    }
   }
 
   rv = channel->AsyncOpen2(this);