Fix incorrectly rendered editor after change font size on guest portal

When editor styles change, Atom notifies only editor components that are
attached to the DOM at the moment of the change. Thus, if the element we
are about to add had already been rendered, we will preemptively clear
all its styling information to ensure it will render correctly even if
some styles changed while it was not attached to the DOM.

lib/guest-portal-binding.js

@@ -155,6 +155,8 @@ class GuestPortalBinding {
     this.newActivePaneItem = newActivePaneItem
 
     if (this.activePaneItem) {
+      this.ensurePaneItemStylesAreUpToDate(newActivePaneItem)
+
       const pane = this.workspace.paneForItem(this.activePaneItem)
       const index = pane.getItems().indexOf(this.activePaneItem)
       pane.addItem(newActivePaneItem, {index, moved: this.addedPaneItems.has(newActivePaneItem)})
@@ -170,6 +172,18 @@ class GuestPortalBinding {
     this.newActivePaneItem = null
   }
 
+  ensurePaneItemStylesAreUpToDate (paneItem) {
+    // When editor styles change, Atom notifies only editor components that
+    // are attached to the DOM at the moment of the change. Thus, if the
+    // element we are about to add had already been rendered, we will
+    // preemptively clear all its styling information to ensure it will render
+    // correctly even if some styles changed while it was not attached to the
+    // DOM.
+    if (this.addedPaneItems.has(paneItem) && paneItem instanceof TextEditor) {
+      paneItem.component.didUpdateStyles()
+    }
+  }
+
   getActivePaneItem () {
     return this.newActivePaneItem ? this.newActivePaneItem : this.activePaneItem
   }