The first report seems similar to  crbug.com/734281 . I wasn't able to repro either. 

+mlamouri, seems like it's related to our usage of media notifications?

Not able to reproduce the issue in the second feedback report on a pixel xl w/ 59.

Able to repro on a Moto M (XT1663) / MRA58K.

Notes:
- Started breaking in 57.0.2987.9
- Only repros in incognito mode

Bisected bug in M58.

Good build: 58.0.2991.0
Bad build:  58.0.2992.0
Regression range:  https://chromium.googlesource.com/chromium/src/+log/58.0.2991.0..58.0.2992.0?pretty=fuller&n=10000

Good commit: 445744
Bad commit:  445745
Culprit CL:  https://chromium.googlesource.com/chromium/src/+/233f53ad273ef485ff5b12510b421a5ab4d429ec

Logs and video at go/chrome-androidlogs1/7/734283.

The stacktrace:

--------- beginning of crash
06-28 05:02:50.174 E/AndroidRuntime(29863): FATAL EXCEPTION: VolumeDialogController
06-28 05:02:50.174 E/AndroidRuntime(29863): Process: com.android.systemui, PID: 29863
06-28 05:02:50.174 E/AndroidRuntime(29863): java.lang.NullPointerException: Attempt to invoke virtual method 'android.media.MediaDescription android.media.MediaMetadata.getDescription()' on a null object reference
06-28 05:02:50.174 E/AndroidRuntime(29863): 	at com.android.systemui.volume.Util.mediaMetadataToString(Util.java:81)
06-28 05:02:50.174 E/AndroidRuntime(29863): 	at com.android.systemui.volume.MediaSessions$MediaControllerRecord.onMetadataChanged(MediaSessions.java:300)
06-28 05:02:50.174 E/AndroidRuntime(29863): 	at android.media.session.MediaController$MessageHandler.handleMessage(MediaController.java:1000)
06-28 05:02:50.174 E/AndroidRuntime(29863): 	at android.os.Handler.dispatchMessage(Handler.java:111)
06-28 05:02:50.174 E/AndroidRuntime(29863): 	at android.os.Looper.loop(Looper.java:207)
06-28 05:02:50.174 E/AndroidRuntime(29863): 	at android.os.HandlerThread.run(HandlerThread.java:61)

 Issue 734281  has been merged into this issue.

Pending fix is reviewed at https://chromium-review.googlesource.com/c/550240

I was able to reproduce the crash on Android O with Pixel:

1. run adb shell setprop log.tag.volume DEBUG
2. adb shell stop
3. adb shell start

Now systemui is restarted and volume dialog will try to log the MediaSession metadata's description when it changes, causing NPE when Chrome sets the metadata to null for incognito tabs.

4. launch Chrome, open an incognito tab
5. go to vimeo.com and play any video

ER: Android doesn't crash, the video is playing
AR: Android shows a dialog indicating systemui has stopped, system UI restarts.

Likely for some reason the motorola/lenovo devices this feedback comes from have this debug logging enabled for some reason :/

Filed b/63096887 for the Android team to fix this on their side too.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5b58af3409b37c9f12ee12c94c947aca1e8598dd

commit 5b58af3409b37c9f12ee12c94c947aca1e8598dd
Author: Anton Vayvod <avayvod@google.com>
Date: Wed Jun 28 22:19:16 2017

[Media,Android] Use empty media metadata instead of null for incognito tabs.

On some Android versions/devices/support library versions, setting null will
cause crash of system UI. Not setting anything might lead to reusing previous
old metadata.

BUG= 734283 
TEST=tentative fix based on stack trace; QA confirmed the APK works.

Change-Id: If5d64f927f67fc16be80f9ef5889b60161a10a29
Reviewed-on: https://chromium-review.googlesource.com/550240
Commit-Queue: Anton Vayvod <avayvod@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#483170}
[modify] https://crrev.com/5b58af3409b37c9f12ee12c94c947aca1e8598dd/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java

It affects Chromes from 57, requesting merges.

This bug requires manual review: We don't branch M61 until 2017-07-20.
Please contact the milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), ketakid @(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The bug is marked as P3 or Feature. It should not be merged as M60 is in beta. 
Please contact the approriate milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), josafat@(ChromeOS), bustamante@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

This is not P3.

Merge approved for M60 branch 3112.  No merge is required for 61, we haven't branched that yet.  In the future, please provide a quick summary of why the change is required to cherry pick, as well as why it's low risk, plus results of testing the change in canary.  See go/chrome-merges for best practices please.

Ah, sorry, my mistake. Is M59 out of question today?

This prevents playing videos from Chrome Incognito tabs on some Android devices (apparently sold in India). The fix on the Chrome side is very small and should be low risk - passing an empty object instead of null to the framework.

We haven't tested on Canary yet, I believe, only locally.
Christine, could you please verify on Canary when 61.0.3144.0 or later is released?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5f1108fb2b2caec96db61b5d445941926913b137

commit 5f1108fb2b2caec96db61b5d445941926913b137
Author: Anton Vayvod <avayvod@google.com>
Date: Thu Jun 29 17:35:06 2017

[Media,Android] Use empty media metadata instead of null for incognito tabs.

On some Android versions/devices/support library versions, setting null will
cause crash of system UI. Not setting anything might lead to reusing previous
old metadata.

BUG= 734283 
TEST=tentative fix based on stack trace; QA confirmed the APK works.
TBR=avayvod@google.com

(cherry picked from commit 5b58af3409b37c9f12ee12c94c947aca1e8598dd)

Change-Id: If5d64f927f67fc16be80f9ef5889b60161a10a29
Reviewed-on: https://chromium-review.googlesource.com/550240
Commit-Queue: Anton Vayvod <avayvod@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#483170}
Reviewed-on: https://chromium-review.googlesource.com/555932
Reviewed-by: Anton Vayvod <avayvod@chromium.org>
Cr-Commit-Position: refs/branch-heads/3112@{#489}
Cr-Branched-From: b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}
[modify] https://crrev.com/5f1108fb2b2caec96db61b5d445941926913b137/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java

M59 is absolutely out of the question, we only have one more beta for M60 left...

Given this, and the fact it's fixed in 60/61, marking as fixed.  Reopen if I'm incorrect here and more work is required.

On 61.0.3144.0, verified able to play videos and there's no crash in youtube.com and vimeo.com in incognito.  Tested on Moto M (XT1663) with M.

Verified fix on Chrome Beta release 60.0.3112.52. No crash observed with playing video's from youtube and vimeo.com in incognito on Moto M(XT1663)

Verified on Moto M(XT1663) with chrome beta release '60.0.3112.66'.