DevTools: rely upon shouldHideOnDetach when considering re-layout of elements and sources panels.

Source/devtools/front_end/sources/SourcesPanel.js

Index: Source/devtools/front_end/sources/SourcesPanel.js
diff --git a/Source/devtools/front_end/sources/SourcesPanel.js b/Source/devtools/front_end/sources/SourcesPanel.js
index 0d8f4a64b4e741ecb7620e6dae71aa4a75160279..882cd682771c301bb7f7c3481149b58b930fce71 100644
--- a/Source/devtools/front_end/sources/SourcesPanel.js
+++ b/Source/devtools/front_end/sources/SourcesPanel.js
@@ -1142,6 +1142,9 @@ WebInspector.SourcesPanel.prototype = {
         if (this.sidebarPaneView && vertically === !this._splitWidget.isVertical())
             return;
 
+        if (this.sidebarPaneView && this.sidebarPaneView.shouldHideOnDetach())
+            return; // We can't reparent extension iframes.
+
         if (this.sidebarPaneView)
             this.sidebarPaneView.detach();
 
@@ -1230,10 +1233,8 @@ WebInspector.SourcesPanel.prototype = {
      */
     _addExtensionSidebarPane: function(pane)
     {
-        if (pane.panelName() === this.name) {
-            this.setHideOnDetach();
+        if (pane.panelName() === this.name)
             this._extensionSidebarPanesContainer.addPane(pane);
-        }
     },
 
     /**