Bug 1536620 return default size in reader mode r=Gijs

Call Reader:ResetZoom only in readermode and make resetFontSize async
***
make resetFontSize async
***
call Reader:ResetZoom only in readermode
***

Differential Revision: https://phabricator.services.mozilla.com/D24445

--HG--
extra : moz-landing-system : lando

browser/base/content/browser-fullZoom.js

@@ -313,15 +313,19 @@ var FullZoom = {
    * @return A promise which resolves when the zoom reset has been applied.
    */
   reset: function FullZoom_reset(browser = gBrowser.selectedBrowser) {
-    let token = this._getBrowserToken(browser);
-    let result = this._getGlobalValue(browser).then(value => {
-      if (token.isCurrent) {
-        ZoomManager.setZoomForBrowser(browser, value === undefined ? 1 : value);
-        this._ignorePendingZoomAccesses(browser);
-      }
-    });
-    this._removePref(browser);
-    return result;
+    if (browser.currentURI.spec.startsWith("about:reader")) {
+      browser.messageManager.sendAsyncMessage("Reader:ResetZoom");
+    } else {
+      let token = this._getBrowserToken(browser);
+      let result = this._getGlobalValue(browser).then(value => {
+        if (token.isCurrent) {
+          ZoomManager.setZoomForBrowser(browser, value === undefined ? 1 : value);
+          this._ignorePendingZoomAccesses(browser);
+        }
+      });
+      this._removePref(browser);
+      return result;
+    }
   },
 
   /**

toolkit/components/reader/AboutReader.jsm

@@ -39,6 +39,7 @@ var AboutReader = function(mm, win, articlePromise) {
   this._mm.addMessageListener("Reader:GetStoredArticleData", this);
   this._mm.addMessageListener("Reader:ZoomIn", this);
   this._mm.addMessageListener("Reader:ZoomOut", this);
+  this._mm.addMessageListener("Reader:ResetZoom", this);
 
   this._docRef = Cu.getWeakReference(doc);
   this._winRef = Cu.getWeakReference(win);
@@ -268,6 +269,10 @@ AboutReader.prototype = {
         this._changeFontSize(-1);
         break;
       }
+      case "Reader:ResetZoom": {
+        this._resetFontSize();
+        break;
+      }
     }
   },
 
@@ -326,6 +331,7 @@ AboutReader.prototype = {
         this._mm.removeMessageListener("Reader:GetStoredArticleData", this);
         this._mm.removeMessageListener("Reader:ZoomIn", this);
         this._mm.removeMessageListener("Reader:ZoomOut", this);
+        this._mm.removeMessageListener("Reader:ResetZoom", this);
         this._windowUnloaded = true;
         break;
     }
@@ -348,6 +354,12 @@ AboutReader.prototype = {
     ReaderMode.leaveReaderMode(this._mm.docShell, this._win);
   },
 
+  async _resetFontSize() {
+    await AsyncPrefs.reset("reader.font_size");
+    let currentSize = Services.prefs.getIntPref("reader.font_size");
+    this._setFontSize(currentSize);
+  },
+
   _setFontSize(newFontSize) {
     this._fontSize = newFontSize;
     let size = (10 + 2 * this._fontSize) + "px";