relevant sample CL: https://chromium-review.googlesource.com/c/chromium/src/+/1168115

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5168c222036a05612abd58658b31e8678b000fec

commit 5168c222036a05612abd58658b31e8678b000fec
Author: Ethan Xu <xuethan@chromium.org>
Date: Mon Nov 19 23:47:07 2018

[WebShareTargetV2] Added support for new share target fields: method, enctype, and fields.

This is the first CL of web share target V2.

The goal of this CL is to add support for three new fields: method, enctype, and fields.
This is in reference to the new web share target spec.
https://pr-preview.s3.amazonaws.com/ewilligers/web-share-target/pull/53.html#share_target-member

The purposes of each field are as follows:
method:  the HTTP method used for launching the web share target. Can be either GET or POST.
enctype: the encoding method used for launching a POST request web share target. Can be
         either application/x-www-form-urlencoded or multipart/form-data.
files:   a sequence of files each containing a name and an accepted sequence of mime types.
         Note that this can only be populated if the method is POST and the enctype is
         multipart/form-data.

Logic checks are performed in manifest_parser.cc to determine if the web share target
has a valid combination of fields.

Bug:  885308 
Change-Id: I277fef7e1402620385cb28909a078eb09676c1fc
Reviewed-on: https://chromium-review.googlesource.com/c/1240867
Commit-Queue: Ethan Xu <xuethan@google.com>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Matt Giuca <mgiuca@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Reviewed-by: Glenn Hartmann <hartmanng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609511}
[modify] https://crrev.com/5168c222036a05612abd58658b31e8678b000fec/content/renderer/manifest/manifest_parser.cc
[modify] https://crrev.com/5168c222036a05612abd58658b31e8678b000fec/content/renderer/manifest/manifest_parser.h
[modify] https://crrev.com/5168c222036a05612abd58658b31e8678b000fec/content/renderer/manifest/manifest_parser_unittest.cc
[modify] https://crrev.com/5168c222036a05612abd58658b31e8678b000fec/third_party/blink/common/manifest/manifest_mojom_traits.cc
[modify] https://crrev.com/5168c222036a05612abd58658b31e8678b000fec/third_party/blink/public/common/manifest/manifest.h
[modify] https://crrev.com/5168c222036a05612abd58658b31e8678b000fec/third_party/blink/public/common/manifest/manifest_mojom_traits.h
[modify] https://crrev.com/5168c222036a05612abd58658b31e8678b000fec/third_party/blink/public/mojom/manifest/manifest.mojom