Sent out the first CL (https://codereview.chromium.org/2257533005/) for review.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ab33c92ba610714412e7a572451bb58e5317c86f

commit ab33c92ba610714412e7a572451bb58e5317c86f
Author: asvitkine <asvitkine@chromium.org>
Date: Tue Aug 30 20:34:19 2016

Change logging of about:flags from actions to a histogram.

This CL deprecates all the "AboutFlags_*" actions and instead
replaces their logging with a AboutFlags.Seen histogram, that
has all the actions as enumerations.

This new histogram is logged using the same code that logs
Login.CustomFlags histogram on ChromeOS. Following this
change, via separate CLs I plan to deprecate Login.CustomFlags
in favor of AboutFlags.Seen and also make the new histogram
get logged on Android, where I think it's currently not logged.

BUG= 639304 

Review-Url: https://codereview.chromium.org/2257533005
Cr-Commit-Position: refs/heads/master@{#415410}

[modify] https://crrev.com/ab33c92ba610714412e7a572451bb58e5317c86f/chrome/browser/about_flags.cc
[modify] https://crrev.com/ab33c92ba610714412e7a572451bb58e5317c86f/chrome/browser/about_flags.h
[modify] https://crrev.com/ab33c92ba610714412e7a572451bb58e5317c86f/chrome/browser/chromeos/login/session/user_session_manager.cc
[modify] https://crrev.com/ab33c92ba610714412e7a572451bb58e5317c86f/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
[modify] https://crrev.com/ab33c92ba610714412e7a572451bb58e5317c86f/tools/metrics/actions/actions.xml
[modify] https://crrev.com/ab33c92ba610714412e7a572451bb58e5317c86f/tools/metrics/actions/extract_actions.py
[modify] https://crrev.com/ab33c92ba610714412e7a572451bb58e5317c86f/tools/metrics/histograms/histograms.xml

Not sure if this newly occurring bug is related: When toggling any flag XYZ and restarting Chrome, it immediately crashes with the following error message and needs to be wiped to get it working again: (note that the flag name is indeed lacking the "--")

08-31 11:46:46.902 24316 24316 F libc    : Fatal signal 6 (SIGABRT), code -6 in tid 24316 (oid.apps.chrome)
08-31 11:46:47.012   221   221 F DEBUG   : *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
08-31 11:46:47.013   221   221 F DEBUG   : Build fingerprint: 'google/volantis/flounder:6.0.1/MOB30W/3031100:user/release-keys'
08-31 11:46:47.013   221   221 F DEBUG   : Revision: '0'
08-31 11:46:47.013   221   221 F DEBUG   : ABI: 'arm'
08-31 11:46:47.013   221   221 F DEBUG   : pid: 24316, tid: 24316, name: oid.apps.chrome  >>> com.google.android.apps.chrome <<<
08-31 11:46:47.013   221   221 F DEBUG   : signal 6 (SIGABRT), code -6 (SI_TKILL), fault addr --------
08-31 11:46:47.048   221   221 F DEBUG   : Abort message: '[FATAL:about_flags.cc(2211)] Check failed: false. ReportAboutFlagsHistogram(): flag 'XYZ@1' has incorrect format.
08-31 11:46:47.048   221   221 F DEBUG   : #00 0xd7ff4d1d /data/app/com.google.android.apps.chrome-1/lib/arm/libbase.cr.so+0x0008ad1d
08-31 11:46:47.048   221   221 F DEBUG   : #01 0xcfc31043 /data/app/com.google.android.apps.chrome-1/lib/arm/libchrome.cr.so+0x0034b043
08-31 11:46:47.048   221   221 F DEBUG   : #02 0xcfa9f93f /data/app/com.google.android.apps.chrome-1/lib/arm/libchrome.cr.so+0x001b993f
08-31 11:46:47.048   221   221 F DEBUG   : #03 0xcfa9f909 /data/app/com.google.android.apps.chrome-1/lib/arm/
08-31 11:46:47.048   221   221 F DEBUG   :     r0 00000000  r1 00005efc  r2 00000006  r3 f7430b7c
08-31 11:46:47.049   221   221 F DEBUG   :     r4 f7430b84  r5 f7430b34  r6 00000009  r7 0000010c
08-31 11:46:47.049   221   221 F DEBUG   :     r8 fff007d8  r9 fff002f8  sl fff007d0  fp ab605488
08-31 11:46:47.049   221   221 F DEBUG   :     ip 00000006  sp fff00290  lr f71bacb1  pc f71bd0a0  cpsr 40070010
08-31 11:46:47.076   221   221 F DEBUG   : 
08-31 11:46:47.076   221   221 F DEBUG   : backtrace:
08-31 11:46:47.076   221   221 F DEBUG   :     #00 pc 000440a0  /system/lib/libc.so (tgkill+12)
08-31 11:46:47.077   221   221 F DEBUG   :     #01 pc 00041cad  /system/lib/libc.so (pthread_kill+32)
08-31 11:46:47.077   221   221 F DEBUG   :     #02 pc 0001b957  /system/lib/libc.so (raise+10)
08-31 11:46:47.077   221   221 F DEBUG   :     #03 pc 00018b09  /system/lib/libc.so (__libc_android_abort+34)
08-31 11:46:47.077   221   221 F DEBUG   :     #04 pc 00016770  /system/lib/libc.so (abort+4)
08-31 11:46:47.077   221   221 F DEBUG   :     #05 pc 00077527  /data/app/com.google.android.apps.chrome-1/lib/arm/libbase.cr.so (_ZN4base5debug13BreakDebuggerEv+22)
08-31 11:46:47.077   221   221 F DEBUG   :     #06 pc 0008af19  /data/app/com.google.android.apps.chrome-1/lib/arm/libbase.cr.so (_ZN7logging10LogMessageD1Ev+556)
08-31 11:46:47.077   221   221 F DEBUG   :     #07 pc 0034b041  /data/app/com.google.android.apps.chrome-1/lib/arm/libchrome.cr.so
08-31 11:46:47.077   221   221 F DEBUG   :     #08 pc 001b993d  /data/app/com.google.android.apps.chrome-1/lib/arm/libchrome.cr.so
08-31 11:46:47.078   221   221 F DEBUG   :     #09 pc 001b9907  /data/app/com.google.android.apps.chrome-1/lib/arm/libchrome.cr.so
08-31 11:46:47.078   221   221 F DEBUG   :     #10 pc 001b9823  /data/app/com.google.android.apps.chrome-1/lib/arm/libchrome.cr.so
08-31 11:46:47.078   221   221 F DEBUG   :     #11 pc 00170fe7  /data/app/com.google.android.apps.chrome-1/lib/arm/libchrome.cr.so
08-31 11:46:47.078   221   221 F DEBUG   :     #12 pc 0017097f  /data/app/com.google.android.apps.chrome-1/lib/arm/libchrome.cr.so
08-31 11:46:47.078   221   221 F DEBUG   :     #13 pc 0067337f  /data/app/com.google.android.apps.chrome-1/lib/arm/libcontent.cr.so (_ZN7content15BrowserMainLoop21PreMainMessageLoopRunEv+46)
08-31 11:46:47.078   221   221 F DEBUG   :     #14 pc 0088faed  /data/app/com.google.android.apps.chrome-1/lib/arm/libcontent.cr.so (_ZN7content17StartupTaskRunner11WrappedTaskEv+24)
08-31 11:46:47.078   221   221 F DEBUG   :     #15 pc 00079fd3  /data/app/com.google.android.apps.chrome-1/lib/arm/libbase.cr.so (_ZN4base5debug13TaskAnnotator7RunTaskEPKcRKNS_11PendingTaskE+122)
08-31 11:46:47.078   221   221 F DEBUG   :     #16 pc 00090f1d  /data/app/com.google.android.apps.chrome-1/lib/arm/libbase.cr.so (_ZN4base11MessageLoop7RunTaskERKNS_11PendingTaskE+200)
08-31 11:46:47.078   221   221 F DEBUG   :     #17 pc 000910bf  /data/app/com.google.android.apps.chrome-1/lib/arm/libbase.cr.so (_ZN4base11MessageLoop21DeferOrRunPendingTaskENS_11PendingTaskE+20)
08-31 11:46:47.078   221   221 F DEBUG   :     #18 pc 0009123d  /data/app/com.google.android.apps.chrome-1/lib/arm/libbase.cr.so (_ZN4base11MessageLoop6DoWorkEv+172)
08-31 11:46:47.078   221   221 F DEBUG   :     #19 pc 000923e1  /data/app/com.google.android.apps.chrome-1/lib/arm/libbase.cr.so (Java_org_chromium_base_SystemMessageHandler_nativeDoRunLoopOnce+104)
08-31 11:46:47.079   221   221 F DEBUG   :     #20 pc 01141fcd  /data/app/com.google.android.apps.chrome-1/oat/arm/base.odex (offset 0xdb8000) (void org.chromium.base.SystemMessageHandler.nativeDoRunLoopOnce(long, long, long)+120)
08-31 11:46:47.079   221   221 F DEBUG   :     #21 pc 01142479  /data/app/com.google.android.apps.chrome-1/oat/arm/base.odex (offset 0xdb8000) (void org.chromium.base.SystemMessageHandler.handleMessage(android.os.Message)+220)
08-31 11:46:47.079   221   221 F DEBUG   :     #22 pc 725645c1  /data/dalvik-cache/arm/system@framework@boot.oat (offset 0x1ec9000)
08-31 11:46:47.461   221   221 F DEBUG   : 
08-31 11:46:47.461   221   221 F DEBUG   : Tombstone written to: /data/tombstones/tombstone_03
08-31 11:46:47.461   221   221 E DEBUG   : AM write failed: Broken pipe

Reverting ab33c92ba610714412e7a572451bb58e5317c86f fixes the crash.

Sorry about this, looking.

Have a fix in the works. Since this is a DCHECK currently, I'm thinking we don't need to revert the original CL since it doesn't affect production - and I plan to land the follow-up fix today.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c1a0c4f2a642dbfb107a454dbc322692c7cf57ee

commit c1a0c4f2a642dbfb107a454dbc322692c7cf57ee
Author: asvitkine <asvitkine@chromium.org>
Date: Wed Aug 31 20:37:39 2016

Fix logging of Launch.FlagsAtStartup histogram.

My initial change was logging the internal value,
rather than the actual switch value. This change
performs the necessary conversion.

BUG= 639304 

Review-Url: https://codereview.chromium.org/2298223002
Cr-Commit-Position: refs/heads/master@{#415741}

[modify] https://crrev.com/c1a0c4f2a642dbfb107a454dbc322692c7cf57ee/chrome/browser/about_flags.cc
[modify] https://crrev.com/c1a0c4f2a642dbfb107a454dbc322692c7cf57ee/components/flags_ui/flags_state.cc
[modify] https://crrev.com/c1a0c4f2a642dbfb107a454dbc322692c7cf57ee/components/flags_ui/flags_state.h

 Issue 541222  has been merged into this issue.

 Issue 622729  has been merged into this issue.

Marking as Fixed.

It appears the histogram does indeed get logged on all platforms, including Android and CrOS - but there is just very few flags seen on CrOS. (Probably because there are very few users on non-stable CrOS channels.)

https://uma.googleplex.com/p/chrome/timeline_v2/?sid=987501e90758069eb2ab90efd5a2fb24

There's a follow up bug here where we want to log values of flags:
https://bugs.chromium.org/p/chromium/issues/detail?id=647330

This is awesome, thanks!  Is there a good baseline for FlagsAtStartup to compare against?  Eg. to answer "what fraction of startups have XXX flag set"?  Should a "total startups" bucket be added to the enum to make this easy?  Or is that perhaps not very useful anyway (eg. some users may have a lot more "startups" than others - especially on Android) and some other analysis is really needed?

To answer comment 13 - you're right, we don't have bucket that just counts startups in that histogram. One could certainly be added - thought it'd be a bit wasteful since right now the histogram is not logged at all for users who don't have any flags.

You could use another histogram that's logged as startup to compare - e.g. the total count of Startup.BrowserMessageLoopStartTime.