crbug.com/769478 too. Maybe this one could be content_shell.

Working to land the changes necessary for content_shell to build.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a750f6b5df4c79c4673e472d1c9b8911a1e68282

commit a750f6b5df4c79c4673e472d1c9b8911a1e68282
Author: Wez <wez@chromium.org>
Date: Thu Oct 26 16:37:42 2017

Only define ContentMainDelegate::Zygote* functions under Linux.

Chromium only uses a "Zygote" process under Linux, but was defining the
ZygoteStarting and ZygoteForked functions for embedders to override for
all OS_POSIX, except Mac & Android. Rather than adding Fuchsia to the
list of exceptions, just fix the definitions to exist only under Linux.

Bug:  772552 
Change-Id: I5d5ede023057c0c52cef29dbb2f79a5185681630
Reviewed-on: https://chromium-review.googlesource.com/738858
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#511847}
[modify] https://crrev.com/a750f6b5df4c79c4673e472d1c9b8911a1e68282/chrome/app/chrome_main_delegate.cc
[modify] https://crrev.com/a750f6b5df4c79c4673e472d1c9b8911a1e68282/chrome/app/chrome_main_delegate.h
[modify] https://crrev.com/a750f6b5df4c79c4673e472d1c9b8911a1e68282/content/app/content_main_runner.cc
[modify] https://crrev.com/a750f6b5df4c79c4673e472d1c9b8911a1e68282/content/public/app/content_main_delegate.cc
[modify] https://crrev.com/a750f6b5df4c79c4673e472d1c9b8911a1e68282/content/public/app/content_main_delegate.h
[modify] https://crrev.com/a750f6b5df4c79c4673e472d1c9b8911a1e68282/content/shell/app/shell_main_delegate.cc
[modify] https://crrev.com/a750f6b5df4c79c4673e472d1c9b8911a1e68282/content/shell/app/shell_main_delegate.h
[modify] https://crrev.com/a750f6b5df4c79c4673e472d1c9b8911a1e68282/headless/lib/headless_content_main_delegate.cc
[modify] https://crrev.com/a750f6b5df4c79c4673e472d1c9b8911a1e68282/headless/lib/headless_content_main_delegate.h

Also landed https://chromium-review.googlesource.com/c/chromium/src/+/737058 which gets content_shell building, but forgot this bug # in the CL description.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f043d56aaeb9aea2274acbfbeb16443bbe6be167

commit f043d56aaeb9aea2274acbfbeb16443bbe6be167
Author: Wez <wez@chromium.org>
Date: Fri Oct 27 22:03:00 2017

Build content_shell & content_browsertests on all Fuchsia bots.

Bug:  772552 
Change-Id: I33137bc6efe8015737e43226f8cb6caeb1c6c1d0
Reviewed-on: https://chromium-review.googlesource.com/740284
Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512304}
[modify] https://crrev.com/f043d56aaeb9aea2274acbfbeb16443bbe6be167/content/shell/app/shell_main_delegate.cc
[modify] https://crrev.com/f043d56aaeb9aea2274acbfbeb16443bbe6be167/testing/buildbot/chromium.fyi.json
[modify] https://crrev.com/f043d56aaeb9aea2274acbfbeb16443bbe6be167/testing/buildbot/chromium.linux.json
[modify] https://crrev.com/f043d56aaeb9aea2274acbfbeb16443bbe6be167/testing/buildbot/gn_isolate_map.pyl

Closing this out since the targets _build_ for Fuchsia; will repurpose issue 769478 for content_browsertests actually running in a meaningful way.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/51b93f4d5c60606a986af6d8614153eeee3cb1a3

commit 51b93f4d5c60606a986af6d8614153eeee3cb1a3
Author: Evgene Gubernatorov <eugenebng@yandex-team.ru>
Date: Thu Nov 30 18:26:49 2017

Small fix for crrev.com/c/738858.

R=wez@chromium.org,rsesek@chromium.org
Bug:  772552 

Change-Id: I666f2ae1ea4a423250b53715b2957d3a87165935
Reviewed-on: https://chromium-review.googlesource.com/787891
Reviewed-by: Wez <wez@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520613}
[modify] https://crrev.com/51b93f4d5c60606a986af6d8614153eeee3cb1a3/chrome/app/chrome_main_delegate.cc