Could you please provide us with a sample test cases of the issue which would help us to triage the issue further.

Thanks in Advance.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3e072f5d6d65ae7d9ee65b5937775eb158871a61

commit 3e072f5d6d65ae7d9ee65b5937775eb158871a61
Author: valih <valih@google.com>
Date: Thu Nov 10 03:59:16 2016

DevTools: introduce "Track CSS Usage" experiment

This patch introduces the "Track CSS Usage" experiment.

The experiment adds a new timeline setting "Track CSS".
When enabled, the timeline recording tracks the usage
of CSS rules and exposes this information through the
Sources panel.

BUG= 663017 

Review-Url: https://codereview.chromium.org/2472213005
Cr-Commit-Position: refs/heads/master@{#431176}

[add] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/LayoutTests/inspector/tracing/highlight-in-source-expected.txt
[add] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/LayoutTests/inspector/tracing/highlight-in-source.html
[add] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/LayoutTests/inspector/tracing/resources/highlight-in-source.css
[modify] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/Source/devtools/BUILD.gn
[add] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/Source/devtools/front_end/components_lazy/CoverageProfile.js
[modify] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/Source/devtools/front_end/components_lazy/module.json
[modify] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/Source/devtools/front_end/main/Main.js
[modify] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js
[modify] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/Source/devtools/front_end/text_editor/cmdevtools.css
[modify] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/Source/devtools/front_end/timeline/TimelineController.js
[modify] https://crrev.com/3e072f5d6d65ae7d9ee65b5937775eb158871a61/third_party/WebKit/Source/devtools/front_end/timeline/TimelinePanel.js

It looks like I cannot set @valih as an owner of this issue.  @caseq can I set you as the owner for now?