Issue 3251 - Add shouldAllowAsync() function for non-urgent policy checks

lib/child/contentPolicy.js

Index: lib/child/contentPolicy.js
===================================================================
--- a/lib/child/contentPolicy.js
+++ b/lib/child/contentPolicy.js
@@ -50,62 +50,95 @@ let collapsedClass = null;
 
 /**
  * Maps numerical content type IDs to strings.
  * @type Map.<number,string>
  */
 let types = new Map();
 
 /**
- * Checks whether a request should be allowed, hides it if necessary
- * @param wnd {nsIDOMWindow}
- * @param node {nsIDOMElement}
- * @param contentType {String}
- * @param location {String}
+ * Processes parent's response to the ShouldAllow message.
+ * @param {nsIDOMWindow} window window that the request is associated with
+ * @param {nsIDOMElement} node  DOM element that the request is associated with
+ * @param {Object|undefined} response  object received as response
  * @return {Boolean} false if the request should be blocked
  */
-function shouldAllow(window, node, contentType, location)
+function processPolicyResponse(window, node, response)
 {
-  let response = sendSyncMessage("AdblockPlus:ShouldAllow", {
-    contentType: contentType,
-    location: location,
-    frames: getFrames(window),
-    isPrivate: isPrivate(window)
-  });
   if (typeof response == "undefined")
     return true;
 
   let {allow, collapse, hits} = response;
+  let isObject = false;
   for (let {frameIndex, contentType, docDomain, thirdParty, location, filter} of hits)
   {
+    if (contentType == "OBJECT")
+      isObject = true;
+
     let context = node;
     if (typeof frameIndex == "number")
     {
       context = window;
       for (let i = 0; i < frameIndex; i++)
         context = context.parent;
       context = context.document;
     }
     RequestNotifier.addNodeData(context, window.top, contentType, docDomain, thirdParty, location, filter);
   }
 
   if (node.nodeType == Ci.nsIDOMNode.ELEMENT_NODE)
   {
     // Track mouse events for objects
-    if (allow && contentType == "OBJECT")
+    if (allow && isObject)
     {
       node.addEventListener("mouseover", objectMouseEventHander, true);
       node.addEventListener("mouseout", objectMouseEventHander, true);
     }
 
     if (collapse)
       schedulePostProcess(node);
   }
+  return allow;
+}
 
-  return allow;
+/**
+ * Checks whether a request should be allowed, hides it if necessary
+ * @param {nsIDOMWindow} window
+ * @param {nsIDOMElement} node
+ * @param {String} contentType
+ * @param {String} location
+ * @return {Boolean} false if the request should be blocked
+ */
+function shouldAllow(window, node, contentType, location)
+{
+  return processPolicyResponse(window, node, sendSyncMessage("AdblockPlus:ShouldAllow", {
+    contentType,
+    location,
+    frames: getFrames(window),
+    isPrivate: isPrivate(window)
+  }));
+}
+
+/**
+ * Asynchronously checks whether a request should be allowed.
+ * @param {nsIDOMWindow} window
+ * @param {nsIDOMElement} node
+ * @param {String} contentType
+ * @param {String} location
+ * @param {Function} callback  callback to be called with a boolean value, if
+ *                             false the request should be blocked
+ */
+function shouldAllowAsync(window, node, contentType, location, callback)
+{
+  sendAsyncMessage("AdblockPlus:ShouldAllow", {
+    contentType,
+    location,
+    frames: getFrames(window),
+    isPrivate: isPrivate(window)
+  }, response => callback(processPolicyResponse(window, node, response)));
 }
 
 /**
  * Actual nsIContentPolicy and nsIChannelEventSink implementation
  * @class
  */
 var PolicyImplementation =
 {
@@ -229,17 +262,17 @@ var PolicyImplementation =
   },
 
   //
   // nsIChannelEventSink interface implementation
   //
 
   asyncOnChannelRedirect: function(oldChannel, newChannel, flags, callback)
   {
-    let result = Cr.NS_OK;
+    let async = false;
     try
     {
       // nsILoadInfo.contentPolicyType was introduced in Gecko 35, then
       // renamed to nsILoadInfo.externalContentPolicyType in Gecko 44.
       let loadInfo = oldChannel.loadInfo;
       let contentType = ("externalContentPolicyType" in loadInfo ?
           loadInfo.externalContentPolicyType : loadInfo.contentPolicyType);
       if (!contentType)
@@ -258,27 +291,31 @@ var PolicyImplementation =
           // seen the original channel yet because the redirect happened before
           // the async code in observe() had a chance to run.
           this.observe(wnd, "content-document-global-created", null, oldChannel.URI.spec);
           this.observe(wnd, "content-document-global-created", null, newChannel.URI.spec);
         }
         return;
       }
 
-      if (!shouldAllow(wnd, wnd.document, types.get(contentType), newChannel.URI.spec))
-        result = Cr.NS_BINDING_ABORTED;
+      shouldAllowAsync(wnd, wnd.document, types.get(contentType), newChannel.URI.spec, function(allow)
+      {
+        callback.onRedirectVerifyCallback(allow ? Cr.NS_OK : Cr.NS_BINDING_ABORTED);
+      });
+      async = true;
     }
     catch (e)
     {
       // We shouldn't throw exceptions here - this will prevent the redirect.
       Cu.reportError(e);
     }
     finally
     {
-      callback.onRedirectVerifyCallback(result);
+      if (!async)
+        callback.onRedirectVerifyCallback(Cr.NS_OK);
     }
   },
 
   //
   // nsIFactory interface implementation
   //
 
   createInstance: function(outer, iid)