|IsMalformed| was introduced because of consuming network bandwidth while uploading "malformed" forms.
https://bugs.chromium.org/p/chromium/issues/detail?id=60422
https://bugs.chromium.org/p/chromium/issues/detail?id=57527 

|FormStructure::IsMalformed| is called from two functions: 
* FormStructure::EncodeQueryRequest we can allow bigger |kMaxFieldsOnTheForm| for this case as queries are sent only when a page is rendered or a dynamic form appeared (see the call hierarchy of AutofillAgent::ProcessForms).
* FormStructure::EncodeQueryRequest we can allow bigger |kMaxFieldsOnTheForm| only if |observed_submission| is true. 

So, we can limit the number of uploads of a big form.

Roger, Sebastien: WDYT?

in #2: the second callsite is FormStructure::EncodeUploadRequest

what value whould you like it to be? Or are you proposing we scrap it entirely?

With query response caching and upload throttling in place, the bandwidth concerns would be mitigated (up to a certain query size) except for forms which grow dynamically.

I would suggest 250 (as I've found a sites that has 222 <input>s, after filtering out some fields is is 179).

I also hope that protos shouldn't consume so much bandwidth as xml did (the issue happened in 2010)

This problem have significant impact on password generation classification. I would consider to merge it back to Beta as the code change would be small. BUT I would merge back with the value of 100 (then it would cover 95% of problem forms)

I have discussed with Maxim that it might make sense to make this parameter finchable. WDYT?

SGTM. Finchable with a default of 250?

Why do these sites have so many fields? I don't want us to be engaging in escalation. I.e., Sites try to not be autofillable by sending more fields, we keep raising the limit. I'd rather just remove the limit in that case.

Their intention was not to have a race but they had maaaany radio buttons:
e.g.
http://my.monsterindia.com/create_account.html
https://sso.ebs.co.kr/idp/join/form.jsp (you may get redirected and select 3 checkboxes before you get to that site)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ca00af373d1cedda85aa03a039fff991f03ccb5d

commit ca00af373d1cedda85aa03a039fff991f03ccb5d
Author: Maxim Kolosovskiy <kolos@chromium.org>
Date: Wed Jul 11 14:16:07 2018

[Autofill] Allow crowdsourcing of big forms

This CL increases |kMaxFieldsOnTheForm| to 100 in |FormStructure::IsMalformed|.
It allows to crowdsource more forms. See the bug for details. Later the
parameter will be increased even more and will be finchable.

UMA histogram is introduced to monitor the size of forms Autofill has to process.

TODO: Finch-controlled threshold and UKM metric.

Bug: 857454
Change-Id: I50c1382dd36e2c707cd34f1a4f139413d9ea6026
Reviewed-on: https://chromium-review.googlesource.com/1131457
Reviewed-by: Roger McFarlane <rogerm@chromium.org>
Reviewed-by: Dominic Battré <battre@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Maxim Kolosovskiy <kolos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574150}
[modify] https://crrev.com/ca00af373d1cedda85aa03a039fff991f03ccb5d/components/autofill/core/browser/form_structure.cc
[modify] https://crrev.com/ca00af373d1cedda85aa03a039fff991f03ccb5d/components/autofill/core/browser/form_structure_unittest.cc
[modify] https://crrev.com/ca00af373d1cedda85aa03a039fff991f03ccb5d/tools/metrics/histograms/histograms.xml

Requesting merge of doubling the maximal number of fields in form that Autofill sends queries for. The change is just increasing the parameter from 48 to 100 fields + adding UMA metric for fields count. 

The change doubles the size of a query Chrome sends to Autofill server. Based on testing, queries will be still less than 1000 bytes. 

Chrome didn't crowdsource the data for some because of this restriction. It is why we don't have data for some forms. 

This bug requires manual review: We are only 11 days from stable.
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), kariahda@(iOS), bhthompson@(ChromeOS), abdulsyed@(Desktop)

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

Approving merge for M68. Branch:3440

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f24e72942eb44a835f2298d02d75199706018391

commit f24e72942eb44a835f2298d02d75199706018391
Author: Maxim Kolosovskiy <kolos@chromium.org>
Date: Mon Jul 16 09:03:19 2018

[Merge-M68] [Autofill] Allow crowdsourcing of big forms

This CL increases |kMaxFieldsOnTheForm| to 100 in |FormStructure::IsMalformed|.
It allows to crowdsource more forms. See the bug for details. Later the
parameter will be increased even more and will be finchable.

UMA histogram is introduced to monitor the size of forms Autofill has to process.

TODO: Finch-controlled threshold and UKM metric.

Bug: 857454
Change-Id: I50c1382dd36e2c707cd34f1a4f139413d9ea6026
Reviewed-on: https://chromium-review.googlesource.com/1131457
Reviewed-by: Roger McFarlane <rogerm@chromium.org>
Reviewed-by: Dominic Battré <battre@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Maxim Kolosovskiy <kolos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574150}

Change-Id: Ic53976ddf92e963119909339ec495938820e4abd
Reviewed-on: https://chromium-review.googlesource.com/1137815
Reviewed-by: Maxim Kolosovskiy <kolos@chromium.org>
Cr-Commit-Position: refs/branch-heads/3440@{#676}
Cr-Branched-From: 010ddcfda246975d194964ccf20038ebbdec6084-refs/heads/master@{#561733}
[modify] https://crrev.com/f24e72942eb44a835f2298d02d75199706018391/components/autofill/core/browser/form_structure.cc
[modify] https://crrev.com/f24e72942eb44a835f2298d02d75199706018391/components/autofill/core/browser/form_structure_unittest.cc
[modify] https://crrev.com/f24e72942eb44a835f2298d02d75199706018391/tools/metrics/histograms/histograms.xml

Maxim, can this bug be marked fixed?

97% fixed.

The threshold is increased to 100 (which covers 97% of forms). Perhaps we want to increase it further with Finch. So, there may be more changes here. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ba5fd2ae8690c6e46f78defdf5401661185f06e7

commit ba5fd2ae8690c6e46f78defdf5401661185f06e7
Author: Maxim Kolosovskiy <kolos@chromium.org>
Date: Tue Dec 11 14:56:19 2018

[Autofill] Increase the limit for the number of fields to 250

According to metrics, 0.3% of forms have >100 fields (the current limit), increase the limit to 250 in order to cover all forms.

Autofill throttling limits the number of queries/uploads are sent for a given form by a given user. Therefore, uploading huge forms wouldn't flood network.

Bug: 857454
Change-Id: Ia92a3d6f2033159df121d8728a263c70ee7914f7
Reviewed-on: https://chromium-review.googlesource.com/c/1369772
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Commit-Queue: Maxim Kolosovskiy <kolos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615523}
[modify] https://crrev.com/ba5fd2ae8690c6e46f78defdf5401661185f06e7/components/autofill/core/browser/form_structure.cc
[modify] https://crrev.com/ba5fd2ae8690c6e46f78defdf5401661185f06e7/components/autofill/core/browser/form_structure_unittest.cc

Pls merge your change to M72 branch 3626 ASAP. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6b7e8e1591be22dad241574de2cd77c3b7103cd3

commit 6b7e8e1591be22dad241574de2cd77c3b7103cd3
Author: Maxim Kolosovskiy <kolos@chromium.org>
Date: Thu Dec 13 06:59:24 2018

[Merge-M72][Autofill] Increase the limit for the number of fields to 250

According to metrics, 0.3% of forms have >100 fields (the current limit), increase the limit to 250 in order to cover all forms.

Autofill throttling limits the number of queries/uploads are sent for a given form by a given user. Therefore, uploading huge forms wouldn't flood network.

Bug: 857454
Change-Id: Ia92a3d6f2033159df121d8728a263c70ee7914f7
Reviewed-on: https://chromium-review.googlesource.com/c/1369772
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Commit-Queue: Maxim Kolosovskiy <kolos@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#615523}(cherry picked from commit ba5fd2ae8690c6e46f78defdf5401661185f06e7)
Reviewed-on: https://chromium-review.googlesource.com/c/1375114
Reviewed-by: Maxim Kolosovskiy <kolos@chromium.org>
Cr-Commit-Position: refs/branch-heads/3626@{#320}
Cr-Branched-From: d897fb137fbaaa9355c0c93124cc048824eb1e65-refs/heads/master@{#612437}
[modify] https://crrev.com/6b7e8e1591be22dad241574de2cd77c3b7103cd3/components/autofill/core/browser/form_structure.cc
[modify] https://crrev.com/6b7e8e1591be22dad241574de2cd77c3b7103cd3/components/autofill/core/browser/form_structure_unittest.cc

The following revision refers to this bug: 
https://chromium.googlesource.com/chromium/src.git/+/6b7e8e1591be22dad241574de2cd77c3b7103cd3

Commit: 6b7e8e1591be22dad241574de2cd77c3b7103cd3
Author: kolos@chromium.org
Commiter: kolos@chromium.org
Date: 2018-12-13 06:59:24 +0000 UTC

[Merge-M72][Autofill] Increase the limit for the number of fields to 250

According to metrics, 0.3% of forms have >100 fields (the current limit), increase the limit to 250 in order to cover all forms.

Autofill throttling limits the number of queries/uploads are sent for a given form by a given user. Therefore, uploading huge forms wouldn't flood network.

Bug: 857454
Change-Id: Ia92a3d6f2033159df121d8728a263c70ee7914f7
Reviewed-on: https://chromium-review.googlesource.com/c/1369772
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Commit-Queue: Maxim Kolosovskiy <kolos@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#615523}(cherry picked from commit ba5fd2ae8690c6e46f78defdf5401661185f06e7)
Reviewed-on: https://chromium-review.googlesource.com/c/1375114
Reviewed-by: Maxim Kolosovskiy <kolos@chromium.org>
Cr-Commit-Position: refs/branch-heads/3626@{#320}
Cr-Branched-From: d897fb137fbaaa9355c0c93124cc048824eb1e65-refs/heads/master@{#612437}