Can't reproduce this so far. Does it happen on any page? Would it be possible for you to attach a screencast?

It was a local problem. I saved on about:blank a 5MB json file in let log and now its permanently saved there. If i type let l, Chromes Dev Tool is automatically showing the content and that need 30 seconds.

Autocomplete in this case should be fixed to collapse the overly long strings like it's done in other places in devtools.

Unable to reproduce the issue on reported chrome version 67.0.3396.99 using Mac 10.12.6. Attaching screen-cast for reference.
Steps: 
---------
1. Launched reported chrome and 
2. Opened Dev tool >> Console
3. Typed let lo
As we are observed that Dev tools working normally. 

@Reporter: Could you please review the attached screen-cast and confirm if anything being missed here.Could you please upgrade to latest chrome 69.0.3492.0, you can download latest chrome builds here: "https://www.chromium.org/getting-involved/dev-channel".let us know if issue still persists or not.

Thanks..!

Deleted: 867940.mp4 3.6 MB

	867940.mp4 3.6 MB View Download

Should we bail out on eagereval here?

Thanks for the request.

Hm, evaluations done by EagerEval, Autocomplete have guards to check and bail out if the string <10k chars.  I suspect that we might need to truncate previews shown in autocomplete's SuggestBox.

OP, could you please try to disable "Autocomplete from history" checkbox [1] and let us know if you can still reproduce this?  I'll look into a fix in the meantime.

[1] https://cdn-images-1.medium.com/max/1000/0*ZggoM0sI_jj1QafW.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/88be57bdf9195e03cf6040911e505addc1d799d8

commit 88be57bdf9195e03cf6040911e505addc1d799d8
Author: Erik Luo <luoe@chromium.org>
Date: Fri Oct 05 22:32:12 2018

DevTools: trim visible autocomplete hint text

Bug:  867940 
Change-Id: If4fdb0c6f0e5a9eab22de9b05e226d215de73026
Reviewed-on: https://chromium-review.googlesource.com/c/1262963
Reviewed-by: Joel Einbinder <einbinder@chromium.org>
Commit-Queue: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597350}
[modify] https://crrev.com/88be57bdf9195e03cf6040911e505addc1d799d8/third_party/blink/renderer/devtools/front_end/text_editor/TextEditorAutocompleteController.js