Version: 54.0.2803.0 74ed884d4d42cb7152dc75fae33351e8e34220cd-refs/heads/master@{#406716} (32/64-bit)
OS: Windows (7,8,8.1,10),Linux (14.04 LTS),Mac OS X(10.10.5, 10.11.4)

What steps will reproduce the problem?
1) Launch chrome , navigate to NTP and open devtools
2) Now go to 'Timeline' section and press 'F5' key from keyboard to record some activity.
3) Now in 'Timeline Data' window click on expand arrow icon to expand 'Main' section and drag it upwards towards Timeline scale,observe(Refer attached screen cast)
 
Actual : Weird overlapping is seen when 'Main' window is dragged upwards towards timeline scale
Expected : Weird overlapping should not be seen when 'Main' window is dragged upwards towards timeline scale

This is a regression issue broken in 'M-51' and below is the manual regression and Narrow bisect info:
Good build : 51.0.2702.0
Bad build : 51.0.2704.0

Narrow bisect info:
https://chromium.googlesource.com/chromium/src/+log/20df67ce971895122441f8cadd473363318b73f2..5f4ec37b6548c11b0b470ce824a3d28f7f54fcd1?pretty=fuller&n=50

Suspecting : r385618 from Narrow bisect 

@caseq : Could you please help to reassign if your change is not the cause for this change.
 

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