Bug 1607754 - Only load about:blank in the devtools frame when switching hosts r=ochameau

Depends on D58238

Differential Revision: https://phabricator.services.mozilla.com/D59132

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

devtools/client/framework/toolbox-host-manager.js

@@ -11,6 +11,7 @@ const L10N = new LocalizationHelper(
 );
 const DevToolsUtils = require("devtools/shared/DevToolsUtils");
 const Telemetry = require("devtools/client/shared/telemetry");
+const { DOMHelpers } = require("devtools/shared/dom-helpers");
 
 // The min-width of toolbox and browser toolbox.
 const WIDTH_CHEVRON_AND_MEATBALL = 50;
@@ -235,6 +236,14 @@ ToolboxHostManager.prototype = {
     const iframe = this.host.frame;
     const newHost = this.createHost(hostType);
     const newIframe = await newHost.create();
+
+    // Load a blank document in the host frame. The new iframe must have a valid
+    // document before using swapFrameLoaders().
+    await new Promise(resolve => {
+      newIframe.setAttribute("src", "about:blank");
+      DOMHelpers.onceDOMReady(newIframe.contentWindow, resolve);
+    });
+
     // change toolbox document's parent to the new host
     newIframe.swapFrameLoaders(iframe);
 

devtools/client/framework/toolbox-hosts.js

@@ -7,7 +7,6 @@
 const EventEmitter = require("devtools/shared/event-emitter");
 const promise = require("promise");
 const Services = require("Services");
-const { DOMHelpers } = require("devtools/shared/dom-helpers");
 
 loader.lazyRequireGetter(
   this,
@@ -82,7 +81,6 @@ BottomHost.prototype = {
     this._browserContainer.appendChild(this.frame);
 
     focusTab(this.hostTab);
-    await createBlankDocument(this.frame);
     this.emit("ready", this.frame);
 
     return this.frame;
@@ -170,7 +168,6 @@ class SidebarHost {
     }
 
     focusTab(this.hostTab);
-    await createBlankDocument(this.frame);
     this.emit("ready", this.frame);
 
     return this.frame;
@@ -279,8 +276,6 @@ WindowHost.prototype = {
         // CSS transitions when switching from docked to window hosts.
         // Added in Bug 832920, should be reviewed in Bug 1542468.
         this.frame.setAttribute("forceOwnRefreshDriver", "");
-
-        this.frame.setAttribute("src", "about:blank");
         resolve(this.frame);
       };
 
@@ -351,7 +346,6 @@ BrowserToolboxHost.prototype = {
 
     this.doc.body.appendChild(this.frame);
 
-    await createBlankDocument(this.frame);
     this.emit("ready", this.frame);
 
     return this.frame;
@@ -427,19 +421,6 @@ function createDevToolsFrame(doc, className) {
   return frame;
 }
 
-/**
- * Load a blank document in the host frame.
- * This is mandatory if the host is created for switching hosts. In that case,
- * the new host's frame needs to have a valid document before we can swap the
- * content of the previous host.
- */
-function createBlankDocument(frame) {
-  return new Promise(resolve => {
-    frame.setAttribute("src", "about:blank");
-    DOMHelpers.onceDOMReady(frame.contentWindow, resolve);
-  });
-}
-
 exports.Hosts = {
   bottom: BottomHost,
   left: LeftHost,