Bug 1386807 - Part 3: Make the UA pref actually disable UA overrides r=Felipe

MozReview-Commit-ID: 25YsSg7P8DP

--HG--
extra : rebase_source : 49766d75008ecb7312fb44de6165d979511c504c

browser/extensions/webcompat/bootstrap.js

@@ -34,12 +34,7 @@ function InjectionsEnablePrefObserver() {
 
 function UAEnablePrefObserver() {
   let isEnabled = Services.prefs.getBoolPref(UA_ENABLE_PREF_NAME);
-  if (isEnabled && !overrider) {
-    overrider = new UAOverrider(UAOverrides);
-    overrider.init();
-  } else if (!isEnabled && overrider) {
-    overrider = null;
-  }
+  overrider.setShouldOverride(isEnabled);
 }
 
 function setDefaultPrefs() {

browser/extensions/webcompat/content/lib/ua_overrider.jsm

@@ -11,6 +11,7 @@ XPCOMUtils.defineLazyServiceGetter(this, "eTLDService", "@mozilla.org/network/ef
 class UAOverrider {
   constructor(overrides) {
     this._overrides = {};
+    this._shouldOverride = true;
 
     this.initOverrides(overrides);
   }
@@ -48,11 +49,26 @@ class UAOverrider {
     }
   }
 
+  /**
+   * Used for disabling overrides when the pref has been flipped to false.
+   *
+   * Since we no longer use our own event handlers, we check this bool in our
+   * override callback and simply return early if we are not supposed to do
+   * anything.
+   */
+  setShouldOverride(newState) {
+    this._shouldOverride = newState;
+  }
+
   init() {
     UserAgentOverrides.addComplexOverride(this.overrideCallback.bind(this));
   }
 
   overrideCallback(channel, defaultUA) {
+    if (!this._shouldOverride) {
+      return false;
+    }
+
     let uaOverride = this.lookupUAOverride(channel.URI, defaultUA);
     if (uaOverride) {
       console.log("The user agent has been overridden for compatibility reasons.");