Indeed, unfortunate! But we can fix this.

Started: https://codereview.chromium.org/2457723004

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6627d6f8dd0ffc0a3f7b3a0fe709d0d368cc81d0

commit 6627d6f8dd0ffc0a3f7b3a0fe709d0d368cc81d0
Author: lushnikov <lushnikov@chromium.org>
Date: Sat Oct 29 04:00:14 2016

DevTools: do not wait for filesystems to create connection.

Today, IsolatedFileSystem.create enumerates all the files in the filesystem
before reporting its creation. The front-end is mostly idle during this
process, since most of the time is spent IPC'ing and reading files in the
IO thread.

Before the "Persistence", we were required to wait for the file systems
before creating targets. However, this is not needed anymore, and we can
let people interact with ElementsPanel and other inspection goodness
rightaway.

BUG= 660425 
R=dgozman, pfeldman

Review-Url: https://codereview.chromium.org/2457723004
Cr-Commit-Position: refs/heads/master@{#428594}

[modify] https://crrev.com/6627d6f8dd0ffc0a3f7b3a0fe709d0d368cc81d0/third_party/WebKit/Source/devtools/front_end/main/Main.js

I've also experienced confusion due to this.  Waiting for seconds with no indication of what is happening is not a great experience.