Only replace widgets that were actually blocked

[ghostwords]

Instead of hypothetically blocked (which doesn't account for page context, for instance).

Fixes pointless first-party replacement (for example).

Should follow #2267.

[ghostwords]

Should adapt 94863c7 following #2438. Needs to be updated to accommodate new users of widgetList.

94863c7.patch

Move replacement widget data loading.

To the place it's used.
---
 src/js/background.js |  6 ------
 src/js/webrequest.js | 31 ++++++++++++++++++++++++-------
 2 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/src/js/background.js b/src/js/background.js
index f79f64851..49dfe6187 100644
--- a/src/js/background.js
+++ b/src/js/background.js
@@ -27,7 +27,6 @@ var pbStorage = require("storage");
 var HeuristicBlocking = require("heuristicblocking");
 var FirefoxAndroid = require("firefoxandroid");
 var webrequest = require("webrequest");
-var widgetLoader = require("widgetloader");
 
 var Migrations = require("migrations").Migrations;
 var incognito = require("incognito");
@@ -50,11 +49,6 @@ function Badger(from_qunit) {
   self.webRTCAvailable = checkWebRTCBrowserSupport();
   self.firstPartyDomainPotentiallyRequired = testCookiesFirstPartyDomain();
 
-  self.widgetList = [];
-  widgetLoader.loadWidgetsFromFile("data/socialwidgets.json", (response) => {
-    self.widgetList = response;
-  });
-
   self.storage = new pbStorage.BadgerPen(async function (thisStorage) {
     self.initializeDefaultSettings();
     self.heuristicBlocking = new HeuristicBlocking.HeuristicBlocker(thisStorage);
diff --git a/src/js/webrequest.js b/src/js/webrequest.js
index 2099e92a6..d477b04c7 100644
--- a/src/js/webrequest.js
+++ b/src/js/webrequest.js
@@ -32,6 +32,7 @@ var constants = require("constants");
 var getSurrogateURI = require("surrogates").getSurrogateURI;
 var incognito = require("incognito");
 var utils = require("utils");
+var widgetLoader = require("widgetloader");
 
 /************ Local Variables *****************/
 let temporaryWidgetUnblock = {};
@@ -513,7 +514,17 @@ let getWidgetBlockList = (function () {
     { key: "allow_once" },
   ];
 
-  return function () {
+  // cached widget list
+  let widgetList;
+
+  // start loading the widget list from disk
+  let widgetListPromise = new Promise(resolve => {
+    widgetLoader.loadWidgetsFromFile("data/socialwidgets.json", response => {
+      resolve(response);
+    });
+  }).catch(console.error);
+
+  return async function () {
     // A mapping of individual SocialWidget objects to boolean values that determine
     // whether the content script should replace that tracker's button/widget
     var widgetsToReplace = {};
@@ -527,7 +538,9 @@ let getWidgetBlockList = (function () {
       }, {});
     }
 
-    badger.widgetList.forEach(function (widget) {
+    widgetList = await widgetListPromise;
+
+    widgetList.forEach(function (widget) {
       // Only replace blocked and yellowlisted widgets
       widgetsToReplace[widget.name] = constants.BLOCKED_ACTIONS.has(
         badger.storage.getBestAction(widget.domain)
@@ -536,7 +549,7 @@ let getWidgetBlockList = (function () {
 
     return {
       translations,
-      trackers: badger.widgetList,
+      trackers: widgetList,
       trackerButtonsToReplace: widgetsToReplace
     };
   };
@@ -612,8 +625,12 @@ function dispatcher(request, sender, sendResponse) {
 
   } else if (request.checkReplaceButton) {
     if (badger.isPrivacyBadgerEnabled(window.extractHostFromURL(sender.tab.url)) && badger.isWidgetReplacementEnabled()) {
-      let widgetBlockList = getWidgetBlockList();
-      sendResponse(widgetBlockList);
+      getWidgetBlockList().then(widgetBlockList => {
+        sendResponse(widgetBlockList);
+      }).catch(console.error);
+
+      // indicate this is an async response to chrome.runtime.onMessage
+      return true;
     }
 
   } else if (request.unblockWidget) {
@@ -760,7 +777,7 @@ function dispatcher(request, sender, sendResponse) {
         });
       }
     });
-    //indicate this is an async response to chrome.runtime.onMessage
+    // indicate this is an async response to chrome.runtime.onMessage
     return true;
 
   } else if (request.type == "uploadCloud") {
@@ -773,7 +790,7 @@ function dispatcher(request, sender, sendResponse) {
         sendResponse({success: true});
       }
     });
-    //indicate this is an async response to chrome.runtime.onMessage
+    // indicate this is an async response to chrome.runtime.onMessage
     return true;
 
   } else if (request.type == "savePopupToggle") {