DevTools: Don't collapse a folder if it has focus on rebind

We shouldn't mess with the folder structure while the user is inside
it. They might be crushed.

Bug: none
Change-Id: Iaa03fc58d2992d849b3fc097747549e938c7761d
Reviewed-on: https://chromium-review.googlesource.com/821560Reviewed-by: Andrey Lushnikov <lushnikov@chromium.org>
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523545}

third_party/WebKit/Source/devtools/front_end/sources/NavigatorView.js

@@ -1634,6 +1634,8 @@ Sources.NavigatorGroupTreeNode = class extends Sources.NavigatorTreeNode {
     if (wasActive === isActive)
       return;
     this._treeElement.listItemElement.classList.toggle('has-mapped-files', isActive);
+    if (this._treeElement.childrenListElement.hasFocus())
+      return;
     if (isActive)
       this._treeElement.expand();
     else