Bug 1472364 - immediately propagate resizes triggered through changing toolbox hosts, r=bgrins

to avoid flicker/delays, immediately enforce we update the size of the inspector once the devtools move from one place to another.

Differential Revision: https://phabricator.services.mozilla.com/D1941

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

devtools/client/inspector/inspector.js

@@ -1269,7 +1269,12 @@ Inspector.prototype = {
    * Handler for the "host-changed" event from the toolbox. Resets the inspector
    * sidebar sizes when the toolbox host type changes.
    */
-  onHostChanged: function() {
+  async onHostChanged() {
+    // Eagerly call our resize handling code to process the fact that we
+    // switched hosts. If we don't do this, we'll wait for resize events + 200ms
+    // to have passed, which causes the old layout to noticeably show up in the
+    // new host, followed by the updated one.
+    await this._onLazyPanelResize();
     if (!this.is3PaneModeEnabled) {
       return;
     }