Things that can be merged include:

WTF/Optional.h
headless/public/util/maybe.h
base/strings/nullable_string16.h

maybe the v8 Nullable class also, though Oilpan considerations are required.

headless/public/util/maybe.h refers to the "V8 Maybe", so that's perhaps another one on the list.

And more...

third_party/WebKit/Source/platform/inspector_protocol/Maybe.h <-- shouldn't that be using WTF::Optional?

Thanks for more pointers, the latter definitely looks like it should.

The generated extensions API types use std::unique_ptr for optional fields.

example: https://code.google.com/p/chromium/codesearch#chromium/src/out/Debug/gen/extensions/common/api/audio.h&l=177

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b2232e6103ff4c902452d9468f543637e091f95b

commit b2232e6103ff4c902452d9468f543637e091f95b
Author: skyostil <skyostil@chromium.org>
Date: Wed Apr 20 14:39:58 2016

headless: Replace headless::Maybe with base::Optional

Covered by existing tests.

BUG= 595353 , 604860 

Review URL: https://codereview.chromium.org/1906493002

Cr-Commit-Position: refs/heads/master@{#388495}

[modify] https://crrev.com/b2232e6103ff4c902452d9468f543637e091f95b/headless/BUILD.gn
[modify] https://crrev.com/b2232e6103ff4c902452d9468f543637e091f95b/headless/lib/browser/types_cc.template
[modify] https://crrev.com/b2232e6103ff4c902452d9468f543637e091f95b/headless/lib/browser/types_h.template
[delete] https://crrev.com/f62311f2c8335dd85071864672d30a149c76c08b/headless/public/util/maybe.h
[delete] https://crrev.com/f62311f2c8335dd85071864672d30a149c76c08b/headless/public/util/maybe_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0a079b3fb27d30609aed6eaaaf2b72423741b5e5

commit 0a079b3fb27d30609aed6eaaaf2b72423741b5e5
Author: danakj <danakj@chromium.org>
Date: Thu Apr 21 00:20:05 2016

Replace WTF::Optional the base::Optional implementation.

R=jbroman, thakis@chromium.org
BUG= 604860 

Review URL: https://codereview.chromium.org/1897863006

Cr-Commit-Position: refs/heads/master@{#388624}

[modify] https://crrev.com/0a079b3fb27d30609aed6eaaaf2b72423741b5e5/third_party/WebKit/Source/platform/graphics/gpu/WebGLImageConversion.h
[modify] https://crrev.com/0a079b3fb27d30609aed6eaaaf2b72423741b5e5/third_party/WebKit/Source/wtf/DEPS
[modify] https://crrev.com/0a079b3fb27d30609aed6eaaaf2b72423741b5e5/third_party/WebKit/Source/wtf/Optional.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7a17ea4bbbeb80ed2091af19d5e90aa40e5e6f9c

commit 7a17ea4bbbeb80ed2091af19d5e90aa40e5e6f9c
Author: petrcermak <petrcermak@chromium.org>
Date: Thu Apr 21 09:58:35 2016

Revert of Replace WTF::Optional the base::Optional implementation. (patchset #9 id:160001 of https://codereview.chromium.org/1897863006/ )

Reason for revert:
This patch broke Android arm64 Builder on chromium.perf: https://bugs.chromium.org/p/chromium/issues/detail?id=605478

Original issue's description:
> Replace WTF::Optional the base::Optional implementation.
>
> R=jbroman, thakis@chromium.org
> BUG= 604860 

TBR=jbroman@chromium.org,esprehn@chromium.org,thakis@chromium.org,danakj@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG= 604860 

Review URL: https://codereview.chromium.org/1908903002

Cr-Commit-Position: refs/heads/master@{#388730}

[modify] https://crrev.com/7a17ea4bbbeb80ed2091af19d5e90aa40e5e6f9c/third_party/WebKit/Source/platform/graphics/gpu/WebGLImageConversion.h
[modify] https://crrev.com/7a17ea4bbbeb80ed2091af19d5e90aa40e5e6f9c/third_party/WebKit/Source/wtf/DEPS
[modify] https://crrev.com/7a17ea4bbbeb80ed2091af19d5e90aa40e5e6f9c/third_party/WebKit/Source/wtf/Optional.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ab29ff6dc90b7b652261f14617e31382f70c31b5

commit ab29ff6dc90b7b652261f14617e31382f70c31b5
Author: liyuqian <liyuqian@google.com>
Date: Thu Apr 28 13:46:15 2016

Replace SkTLazy with base::Optional

BUG= 604860 
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/1925433002
Cr-Commit-Position: refs/heads/master@{#390364}

[modify] https://crrev.com/ab29ff6dc90b7b652261f14617e31382f70c31b5/cc/playback/image_hijack_canvas.cc
[modify] https://crrev.com/ab29ff6dc90b7b652261f14617e31382f70c31b5/cc/playback/raster_source.cc
[modify] https://crrev.com/ab29ff6dc90b7b652261f14617e31382f70c31b5/skia/ext/benchmarking_canvas.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f337675ea340b9d2070e773ec4c14a8e179c78ab

commit f337675ea340b9d2070e773ec4c14a8e179c78ab
Author: danakj <danakj@chromium.org>
Date: Fri Apr 29 05:34:46 2016

Replace WTF::Optional the base::Optional implementation.

R=jbroman, thakis@chromium.org
BUG= 604860 

Committed: https://crrev.com/0a079b3fb27d30609aed6eaaaf2b72423741b5e5
Cr-Commit-Position: refs/heads/master@{#388624}

Review-Url: https://codereview.chromium.org/1897863006
Cr-Commit-Position: refs/heads/master@{#390594}

[modify] https://crrev.com/f337675ea340b9d2070e773ec4c14a8e179c78ab/build/common.gypi
[modify] https://crrev.com/f337675ea340b9d2070e773ec4c14a8e179c78ab/build/config/compiler/BUILD.gn
[modify] https://crrev.com/f337675ea340b9d2070e773ec4c14a8e179c78ab/third_party/WebKit/Source/platform/graphics/gpu/WebGLImageConversion.h
[modify] https://crrev.com/f337675ea340b9d2070e773ec4c14a8e179c78ab/third_party/WebKit/Source/wtf/DEPS
[modify] https://crrev.com/f337675ea340b9d2070e773ec4c14a8e179c78ab/third_party/WebKit/Source/wtf/Optional.h

This issue has been available for more than 365 days, and should be re-evaluated. Please re-triage this issue.
The Hotlist-Recharge-Cold label is applied for tracking purposes, and should not be removed after re-triaging the issue.

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

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/86419ce069bfc9718a8b374f192cdb28ecd6f414

commit 86419ce069bfc9718a8b374f192cdb28ecd6f414
Author: Sam McNally <sammc@chromium.org>
Date: Tue May 23 03:24:34 2017

Change NullableString16 to wrap a base::Optional<base::string16>.

This allows the existing mojo traits for string16 to be reused for
NullableString16.

Bug: 577685, 604860 
Change-Id: I69a7be9e14c033ca2c7ab92e7cc0078eaa8a391a
Reviewed-on: https://chromium-review.googlesource.com/509669
Commit-Queue: Sam McNally <sammc@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#473800}
[modify] https://crrev.com/86419ce069bfc9718a8b374f192cdb28ecd6f414/base/strings/nullable_string16.cc
[modify] https://crrev.com/86419ce069bfc9718a8b374f192cdb28ecd6f414/base/strings/nullable_string16.h

Marking this as it looks like some of the types have been removed (like in headless/ or are based on base::Optional now). Some code use some mechanism that could be replaced in favour of base::Optional but I don't think we want a bug to go hunt for all these places.