I used a patch from noyau, made similar changes elsewhere and I have EG compiling with deployment set to 10.0.

There was a couple of test failures, I need to investigate if these normally fail or if I broke something.

You can follow along on the issue here:
https://github.com/google/EarlGrey/issues/643

Here's an in progress patch:
https://github.com/google/EarlGrey/pull/646

github CL has landed, here is a CL to roll it into Chromium:
https://chromium-review.googlesource.com/c/chromium/src/+/731893

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/47b89c5b265209b533528ef604ca3d99ca4078de

commit 47b89c5b265209b533528ef604ca3d99ca4078de
Author: Mike Baxley <baxley@chromium.org>
Date: Mon Oct 23 21:13:49 2017

Roll ios/third_party/earl_grey b8f1ed850b..2fd8a7d4b7.

This provides support to build with deployment target 10.0.

Bug:  774724 ,  774726 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I8d98edee18252984fbab35fb8171294dd8eac235
Reviewed-on: https://chromium-review.googlesource.com/731893
Commit-Queue: Mike Baxley <baxley@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510914}
[modify] https://crrev.com/47b89c5b265209b533528ef604ca3d99ca4078de/DEPS
[modify] https://crrev.com/47b89c5b265209b533528ef604ca3d99ca4078de/ios/third_party/earl_grey/BUILD.gn
[modify] https://crrev.com/47b89c5b265209b533528ef604ca3d99ca4078de/ios/third_party/earl_grey/README.chromium

It rolled and we have a few good builds, so closing as Fixed. noyau@ re-open and let me know if something doesn't work when you up the version to 10.0.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9723f2a70e3b4e86b10917eded365c1f9465b807

commit 9723f2a70e3b4e86b10917eded365c1f9465b807
Author: Gregory Chatzinoff <gchatz@chromium.org>
Date: Mon Oct 23 23:54:45 2017

Revert "Roll ios/third_party/earl_grey b8f1ed850b..2fd8a7d4b7."

This reverts commit 47b89c5b265209b533528ef604ca3d99ca4078de.

Reason for revert: This CL broke downstream External URL
tests.

Original change's description:
> Roll ios/third_party/earl_grey b8f1ed850b..2fd8a7d4b7.
> 
> This provides support to build with deployment target 10.0.
> 
> Bug:  774724 ,  774726 
> Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
> Change-Id: I8d98edee18252984fbab35fb8171294dd8eac235
> Reviewed-on: https://chromium-review.googlesource.com/731893
> Commit-Queue: Mike Baxley <baxley@chromium.org>
> Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
> Reviewed-by: Gauthier Ambard <gambard@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#510914}

TBR=noyau@chromium.org,sdefresne@chromium.org,baxley@chromium.org,gambard@chromium.org

Change-Id: I83b264de474a13a21b9c20554d7812f99518fd02
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  774724 ,  774726 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Reviewed-on: https://chromium-review.googlesource.com/734337
Reviewed-by: Gregory Chatzinoff <gchatz@chromium.org>
Commit-Queue: Gregory Chatzinoff <gchatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510965}
[modify] https://crrev.com/9723f2a70e3b4e86b10917eded365c1f9465b807/DEPS
[modify] https://crrev.com/9723f2a70e3b4e86b10917eded365c1f9465b807/ios/third_party/earl_grey/BUILD.gn
[modify] https://crrev.com/9723f2a70e3b4e86b10917eded365c1f9465b807/ios/third_party/earl_grey/README.chromium

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c1441e7a1fdc5a7b654103608bdabb3bb11901a6

commit c1441e7a1fdc5a7b654103608bdabb3bb11901a6
Author: Mike Baxley <baxley@chromium.org>
Date: Fri Nov 03 18:26:47 2017

Roll ios/third_party/earl_grey b8f1ed850b..2fd8a7d4b7.

This provides support to build with deployment target 10.0.

Bug:  774724 ,  774726 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ic6445cb9bb788fbc92b90caa511473ea2ad963c6
Reviewed-on: https://chromium-review.googlesource.com/753645
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Mike Baxley <baxley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513844}
[modify] https://crrev.com/c1441e7a1fdc5a7b654103608bdabb3bb11901a6/DEPS
[modify] https://crrev.com/c1441e7a1fdc5a7b654103608bdabb3bb11901a6/ios/third_party/earl_grey/BUILD.gn
[modify] https://crrev.com/c1441e7a1fdc5a7b654103608bdabb3bb11901a6/ios/third_party/earl_grey/README.chromium