Thanks for the report.

dbloch@, are you still seeing this issue?  If so, can you provide a bug report or any details that got you into that state?  We haven't been able to repro with the steps.

It would help me to see a video of the repro.  Small details like whether a scrollbar is shown or not might help me understand the root cause.

I also suggest trying flows that create CCT in between switching to Chrome tabs in case that is required to repro.

I'm no longer seeing it.  Maybe fixed in 61.0.3063.0?

Thanks.

Thanks for the update.

Closing this issue as per comment #5.

Thanks!!

Have seen broken scrolling issue on Canary with these steps:

1.  Have some tabs open.
2.  Swipe away Chrome from Recents.
3.  Re-launch Chrome.
4.  Switch tabs (by swiping between tabs or using tab switcher)
5.  Scroll up/down with finger held down.
6.  Repeat steps 3 and 4 a couple times, if needed

Notes:
- Bug is not consistent with steps above
- Seen it on Pixel/Pixel XL on O and N
- Fling works fine
- Links are clickable on the page
- Video and logcat are at go/chrome-androidlogs1/7/747733

This issue doesn't seem easy to bisect. 
I have been trying for over a day now and I keep getting different results. I have observed that its easier to hit in recent builds (M62) compared to M61 builds. Ex., On 61.0.3149.0, the issue didn't repro at first but it did after trying several times.

The scroll bar is not visible when scroll is disabled. It shows up during fling (which works).
Let me know if I can provide any other info. 

Jinsuk will try to investigate.  Because only drag-scroll is broken, maybe it's in his area (browser not issuing ScrollUpdate events perhaps?)

I think taking a chrome://tracing trace during the nonworking scroll gesture might help a lot to understand the cause.

No luck repro'ing the issue so far. The closest thing I can get is drag-scroll not working on a tab in the newly opened Chrome (after removing it from the Android recents) when it is still showing the snapshot thumbnail. But the scroll starts working fine once the page finishes loading. The problem that fling works while drag-scroll doesn't has never happened to me (yet). I'll keep looking to find more clues / repro it.

OK I found a step that always reproduces the issue. While a tab is loading a page with its thumbnail snapshot on the screen, "fling" the page (so steps at #7 almost works, except you should fling the page before step 5 to reproduce it). The fling won't work which is kind of expected but this makes drag-scroll stop working even after the page finishes loading, while fling starts working.

Bisect points that the culprit is r479871 for  Issue 730197  which drops scroll event on certain situations. sahel@ would you be able to take care of this, given that you are more familiar with the flow/background?

Thanks for the bisect!  There's no evidence r479871 fixed a serious bug and the true fix may be hard to find, and it looks like this reverts cleanly.  Jinsuk, could you revert and cherry-pick the revert, so sahel@ can take his time to fix and reland?

Will do. sahel@ I hope you don't mind having it reverted. 

The revert patch applies cleanly but unfortunately it breaks several tests:

https://chromium-review.googlesource.com/c/607729

SitePerProcessBrowserTest.ScrollBubblingFromOOPIFTest

org.chromium.content.browser.ContentViewScrollingTest#testOnScrollChanged
org.chromium.content.browser.ContentViewScrollingTest#testScrollTo
org.chromium.content.browser.ContentViewScrollingTest#testJoystickScroll
org.chromium.content.browser.ContentViewScrollingTest#testFling
org.chromium.content.browser.ContentViewScrollingTest#testScrollBy
org.chromium.content.browser.ContentViewScrollingTest#testOverScroll

I'm afraid this still needs further investigation by sahel@. 

The comment 12 produces the bug correctly, but reverting the cl is not necessary, the below cl fixes the bug:
https://chromium-review.googlesource.com/c/601169

The problem is that if a scroll gets ignored and a fling happens after that, then the ignore_scroll flag won't be reset since no GSE happens if a fling starts.
The fix resets the ignore_scroll flag on GSB.