Tested the issue in Android and able to reproduce the issue. 

Steps Followed:
1. Auto rotate is enabled on the device and launch the Chrome Browser.
2. Navigate to the URL: http://easyhtml5video.com/
3. Play any video and open in the full screen mode.
4. Turn the device into landscape mode.
5. Turn device into portrait mode.
6. Observed that full screen mode is exit.

Chrome versions tested:
64.0.3282.137 (Stable), 66.0.3336.4(Canary)

OS:
Android 8.1.0

Android Devices:
Pixel XL

Using the per-revision bisect providing the bisect results,
Good Build - 61.0.3139.0 (481757)
Bad Build - 61.0.3140.0 (482096)  

You are looking for a change made after 482071(GOOD), but before 482072(BAD).


CHANGELOG URL:
The script might not always return single CL as suspect as some perf builds might get missing due to failure.
https://chromium.googlesource.com/chromium/src/+/a9613b5edbee77c0b668743018b495cb50ca0d0c

From the CL above, assigning the issue to the owner concerned.

@mlamouri:  Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to owner concerned.

Please navigate to below link for log's and video--
go/chrome-androidlogs/808095

Note: 
1. This issue is not observed in Desktop.
2. This issue is not seen on mobile FireFox.

The steps in comment #2 are Working As Intended. I'm not entirely certain if they are the same as the original ones given that there is the step 7 that is missing.

I couldn't reproduce following the original comment either.

pnangunoori@ can you PTAL?

mlamouri@ -- Issue is still observed in latest Stable #64.0.3282.137 and Canary #66.0.3341.0 on Pixel Android 8.1.0.

Steps provided in C#2 and original comment are the same, but just tried to elaborate the steps.

Please refer the file '808095-ChromeVSFireFox.mp4' from go/chrome-androidlogs/808095

Summary of the issue - When a video is being played in the full screen mode (in landscape mode) and if the device is turned to portrait mode, full screen mode of the video gets exit.

Thanks!

This is working as intended.

I'm not trying to convince you that exiting fullscreen after rotating device to portrait mode is a bug (I thought it is a feature from the very beginning). But exiting fullscreen without any user action immediately after going to fullscreen second time is indisputable bug. I believe that you can't reproduce it using Pixel, I have access to devices where this bug occur and ones where it doesn't. I'm able to induce this bug on Samsung Galaxy S8, Huawei P10 and Huawei P9 Lite. I'll try to post here some video tomorrow.

Regards, Matt.

Video I promised: https://www.youtube.com/watch?v=jb3h8NXgfCw

I checked it again and Huawei P10 seems to work OK.

List of devices WITH this bug I was able to test:

1. Samsung Galaxy S8
2. Huawei P9 Lite
3. MyPhone Luna

List of devices WITHOUT this bug I was able to test:

1. Nexus 5X
2. Pixel 2
3. HTC Desire 825
4. Huawei P9
5. Huawei P10
6. Samsung Galaxy S4