I just updated to Chrome Version 49.0.2623.110 m, and it seems to have solved some of the issue, however I still see the issue at-hand when hovering over a variable that is undefined.

I just tried to hover over "undefined" variable and everything worked fine on Chrome 52.0.2706.0. Could you please try this in Chrome Canary?

Have had the same issue as described in the initial bug report.
My UserAgent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.75 Safari/537.36

I found a work around that may be able to pinpoint the problem:
My default font setting is set at 90%. When hovering over a primitive type variable, the tool-tip is unreadable. After setting font back to 100% or larger, the tool-tip is readable. Bug can also be replicated by pressing Ctrl + mouse wheel to alter the font size.

I can confirm this is happening. To recreate zoom out a bit ( ctrl - ) and hover over undefined variable.

 Issue 614269  has been merged into this issue.

Yes I have this same issue in latest version of chrome with Windows 10, for both undefined variables and other.

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In developer tools, press "ctrl + 0" to solve the problem. 

You my dear friend are correct. I guess the problem is when you are zoomed out.

I have this issue with default zoom level (ctrl+0), but when I increase the zoom by 1 level (ctrl + plus). it works fine for me.

 Issue 623064  has been merged into this issue.

Thanks for the temp fix on this. From 100% I zoom out to 110% and all fixed!

I still consider this as a bug, Why should i fix this via zooming my editor to 110%. 
Actually for me it is fixed when I'm zoomed out to 50% I can see the value.
This should be simple css fix to resolve this. 
If only I'd know how to fix this by myself. 
Should I write some plugin or something?

Who wrote this is not a bug? It is a bug, or else the status would have been WontFix.

You can run the Developer Tools feature on the Developer Tools feature by undocking the Developer Tools and pressing Control + Shift + J.
(The front end of the Developer Tools feature is written in HTML, JavaScript and CSS)
If you find the way to resolve it, you can either contribute a patch, or even give some lead (or actual code changes) here and I guess someone could make a patch of it.

So It seems it is fixed in chrome dev tools in dark theme.
Settings -> Preferences -> Appearance and theme Dark...

Now it's fine, although I don't like the black theme (:

For reference, I was able to repro on Linux with Chrome 56.0.2890.0 after zooming out 3 levels and hovering on an undefined variable.  Bug was not observed on null variables.

After some investigation, it seems that the root cause of this issue is that the scrollbar should be removed when it isn't.  Another bug covers this:  crbug.com/633602 

I've made a small standalone repro case in the attachment.

The symptom for DevTools can be likely be fixed by changing the css.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/35a2db47116994f527950d9bac81873a9661c096

commit 35a2db47116994f527950d9bac81873a9661c096
Author: luoe <luoe@chromium.org>
Date: Thu Oct 20 00:18:53 2016

DevTools: popovers use padding instead of margin

The root cause of this issue is  crbug.com/633602 , which leads to cases when
scrollbars are not removed from elements even though the content would fit. In
our case, popovers with only one line of content will exhibit a scrollbar on
certain zoom levels before we apply their correct width/height.

By using padding instead of margins, the inner content has extra height and no
scrollbar, even before its fixed width/height is applied.

BUG= 599214 

Review-Url: https://chromiumcodereview.appspot.com/2422413002
Cr-Commit-Position: refs/heads/master@{#426348}

[modify] https://crrev.com/35a2db47116994f527950d9bac81873a9661c096/third_party/WebKit/Source/devtools/front_end/animation/AnimationTimeline.js
[modify] https://crrev.com/35a2db47116994f527950d9bac81873a9661c096/third_party/WebKit/Source/devtools/front_end/ui/Popover.js
[modify] https://crrev.com/35a2db47116994f527950d9bac81873a9661c096/third_party/WebKit/Source/devtools/front_end/ui/SwatchPopoverHelper.js
[modify] https://crrev.com/35a2db47116994f527950d9bac81873a9661c096/third_party/WebKit/Source/devtools/front_end/ui/popover.css